Apple’s sixth-generation iPhone — due later this year — is expected to represent a significant physical diversion from the handset’s current design. Inside and out, the next flagship promises to be radical and revolutionary, with the potential to feature new and updated tech at every turn. However, before trying to predict exactly what’s coming, I thought it would be prudent to make a comprehensive list of what could be in store for the line’s immediate future.

Naturally, not everything on this list will come to pass in 2012, and it’s important to look at each item in the light of Apple’s ever-shrinking elbow-room in the mobile arena of material change. Like we saw with the new iPad, even significant upgrades are likely to be similar on the surface to what we’ve already seen. In terms of form factor, the iPad’s design has very little leeway going forward. The iPhone’s evolution is not far behind.

In practical terms, the iPhone has time enough for one last radical revision. Come fall, Apple will likely revert from the flat-backed appearance of its fourth- and fifth-generation handsets to the curvaceous lineage established with the first three iPhones and two most recent iPads.

Based on the safe assumption that Apple’s unlikely to unveil multiple headlining changes at once (to preserve the all-important feeling of “new” as yearly iterations become more and more aesthetically staid), it’s probably politic to pick what you consider the most pertinent few advances from the following selection:

The New iPhone

Most people expect the new iPhone to follow the iPad’s lead and officially drop the suffix. Because Apple will continue selling three concurrent generations of their world-beating handset, the simplified moniker could prove slightly (more) problematic for marketing purposes. But, in the interest of simplicity and unity, it’s a good bet that the new iPhone will just be the new iPhone. Against all odds, I got my wish with the new iPad. Lightning can strike twice!

LTE Antenna

This one needs no introduction and no explanation. LTE’s already in the new iPad, and it’s a no-brainer for the new iPhone. Otherwise, you can pretty much rest assured you’ll get the now-standard all-in-one “world phone” experience with the iPhone’s quad-band GSM/GPRS/EDGE + Dual-band CDMA/EV-DO Rev A radio chipset. (For other connectivity options, it’s safe to say you’ll get the familiar 802.11 b/g/n + Bluetooth 4.0 array.)

Denser, More Powerful Battery

Arguably the new iPad’s most significant advancement, Apple’s new, denser battery technology should make its way into the company’s next iPhone. Because this iPhone won’t have a drastically increased system load like the new iPad did (beyond its new LTE radio), the iPhone will benefit from the new battery by offering increased run-times. This is particularly important in the handset industry, and it should give Apple yet another leg up on its competition.

Fall Release Window

Also a no-brainer. Apple’s not going to cut the bestselling handset in history short by bumping it to the back shelf after just eight or nine months. Last year, the fall iPhone release was an exception. This year — and for many more — it’ll be the rule.

3.70- to 4-inch display

While certain rumors are obviously wrong, Apple will likely increase the iPhone’s display size this time around. The writing on the wall is clear: Releasing another 3.5-inch iPhone would be a PR nightmare. Therefore, in the interest of keeping its Retina branding meaningful, Apple has a choice to make. The company could keep its existing assembly-line fabrication process intact and simply make larger panels at the iPhone’s current 326 PPI. Of course, this would adversely affect the established presentation of every single app in the App Store, and Apple is historically loath to so rake its developers over the coals. Instead, Apple will almost certainly stretch the screen out — It is simply a question of how far and at what cost.

If Apple keeps the iPhone’s current aspect ratio (3:2) and pixel count (960 x 640), each jump in diagonal size would reduce the screen’s PPI. Since Steve Jobs famously called 300 PPI the Retina “minimum,” Apple can expand the iPhone’s display to only 3.85 inches without breaking the spirit of what Retina stands for. At 3.70 inches (as rumored by some), the iPhone would have a pixel density of just under 312 PPI, while a four-inch display (as rumored by others) would be just over 288 PPI. For more incremental PPIs, see the chart below:

Screen size and corresponding PPI.

Of course, the new iPad’s Retina display is much less dense at 264 PPI, but Apple’s justification — that users typically hold their iPads farther away from their faces — neatly swept all incongruity under the rug. As far as density goes, I can’t see much of a difference between my iPhone 4 and my new iPad, and I suspect Apple could comfortably drop beneath that 300 PPI barrier with minimal backlash. Retina’s just marketing, anyways. (For the curious, if the new iPhone were to use the new iPad’s display, its screen would be a whopping 4.37 inches! It could happen, but that would drastically violate the tenets of one-handed usability upon which Apple settled for the original iPhone’s screen size).

I expect a jump, but not beyond 3.85 inches. All things considered, that seems to be the logical maximum.

As for screen technology, Samsung claims Apple’s going OLED. Unless OLED panels are finally less expensive to manufacture than Apple’s current TFT LCD panels, I doubt they’d make the leap. Yeah, OLEDs might be a little less power hungry and a tiny bit easier to see outdoors, but Apple’s not at all in dire straights when it comes to charge longevity, and if the screen’s too dark, you can always turn up the brightness.

Reduced Bezel Width

While the iPad’s bezel is pretty much fixed by human anatomy (We have fat thumbs!), the iPhone can definitely afford to slim up a bit. In the interest of packing its larger display into as similarly-sized a body as possible, Apple will likely give us a display with extremely thin side bezels. However, the top and bottom bezels will still need to accomodate other hardware. They’ll probably be reduced, but don’t expect them to go away.

Rounded Form Factor

Even before the iPhone 4S came out, rumors had it that the flat form factor of the iPhone 4 had “fallen out of favor” with Apple executives. Also prior to the 4S, every indication was that Apple was prepping a return to the curved-back stylings of the iPhone 3GS. Indeed, the last two generations of iPad also indicate a Jony Ive-led shift away from the famous flat edges of original iPad. Because of this, I expect the new iPhone’s overall shape to fall somewhere in between the iPhone 3GS and new iPad. Like its big brother, the iPhone’s rear panel may be shaped of aluminum, though it’s not out of the question that Apple might finally put those glass-carvers to good use and give us something really special. Heck, they might even consider a unibody carbon fiber design, though that technology will probably come to Cupertino’s laptops first.

A5X Processor

So far, Apple’s M.O. has been to release a new processor for the iPad before carrying it over to the new iPhone later in the year. That seems unlikely to change, as the A5X SoC already has enough oomph to do everything you’d need on the small (albeit slightly bigger) screen. The quad-core A6, then, will probably launch inside the fourth-generation iPad next March and be one of the main selling-points of the 2013 iPhone. There isn’t any practical reason to hasten that process.

10MP Rear Camera

The next iPhone will surely sport a bigger, better (iSight?) camera. I don’t have any evidence to support such, but it fits with Apple’s history over the last few years. The technology is certainly there, and people consider a smartphone’s camera to be an important part of the overall package. Look for Apple to fit a bigger sensor into the iPhone’s backside, but don’t expect a dual flash or 3D support or anything like that. A 10MP module outfitted with Apple’s proprietary five-lens system should be more than sufficient to take excellent photographs. Larger MP units, while available, will probably be pocketed for future inclusion.

HD FaceTime Camera

Most folks expected a high-definition front-facing camera in the new iPad and were surprised to find that familiar VGA unit included instead. Of course, Apple might actually be saving its improved FaceTime camera for the iPhone. After all, that’s where FaceTime itself initially launched. Still, on the iPhone’s smaller screen, you don’t really need the enhanced resolution HD FaceTime affords, so I doubt the next iPhone will have the feature onboard. Again, Apple can save this for next time, when it’ll need many small changes to counter the iPhone’s sure-to-be fixed future physical look.

Increased RAM

The new iPad features 1 GB of RAM, whereas both the iPhone 4 and 4S only offer 512 MB. It seems high time Apple gives the iPhone a memory boost. But RAM is power-hungry, and increasing the iPhone’s supply will impact its battery life to some (hopefully small) extent. Apple can get away with keeping its new iPhone at 512 MB, but I think they might surprise us with an entire gigabyte. Since Apple doesn’t advertise RAM to begin with, I don’t think they’ll resort to using it as a marketable feature in the future. They might as well give it to us now.

“Micro” Dock Connector

This is a popular rumor, and it’s likely a sure thing somewhere down the road. However, since the 30-pin connector is currently a multi-billion-dollar business for Apple, the company may not be ready to ditch it just yet. Yes, it would free up some space internally, but that may not be as pressing a factor as many think. Remember, the iPhone is probably getting bigger anyways, and that alone might afford Apple all the space it needs. Plus, altering the dock would — in my estimation — amount to an aforesaid headlining change, and Apple may need that Ace for another year when physical change is not in cards.

When Apple does change its dock, though, there’s no telling exactly what technology will be used in its place. Thunderbolt? USB 3.0? With MagSafe? Who knows!

NFC Support

One day. NFC terminals aren’t nearly ubiquitous enough to be considered for inclusion in the upcoming iPhone. They may never be. But even if Apple spearheads some campaing to get nationwide businesses and retail stores on board, it’ll take a year or two before NFC becomes a viable option. Right now, it’s still very much a fringe technology.

Capacitive Home Key

Everyone’s been clamoring for Apple to ditch the physical Home button, but it’s not happening right now. Accidental input is already a problem with the current physical key, and it would only be exacerbated by a capacitive solution. Plus, it would need to draw power to function properly, and the iPhone’s battery (better though it will obviously be) can ill-afford to bear any unnecessary burden. The sole seeming benefit — that it represents one less part to break — wouldn’t outweigh the pair of aforementioned cons.

If Apple actually figures out an efficient and UX-appropriate application for a capacitive Home key, it’ll come out some other year. Like several other listed advancements (micro dock, HD FaceTime camera, NFC chip), Apple is better off incubating this particular feature and using it as a headlining upgrade a year or two from now.

Stereo Speakers

This could be another key selling point for future generations, but I doubt we’ll see stereo speakers any time soon. They’re not particularly necessary, and you’d think they’d debut in the iPad — a far more media-centric device — first.

Nano SIM Support

Not yet. Apple’s caught up in a contentious battle for SIM superiority, and it’s going to be some time before the standards — whatever they become — are agreed upon and implemented.

Inductive Charging

Inductive charging — at least in the sense of being able to lay a handset down on some electrified mat or device and have it start filling up the battery — is not going to happen. It’s a gimmick more than anything, and it requires additional parts to function. It would effectively break the iPhone’s lauded simplicity to bundle the handset with an unnecessarily bulky (and notoriously inefficient) charging mechanism. Palm’s Touchstone was neat, but it wasn’t even slightly practical. Apple’s MagSafe technology is a far more sensible solution.

“Static” Haptics

No. Or, if you like, in all-caps: NO.

Give it five years.

And even then, maybe not.

So, What’ll It Be?

I don’t know for sure. If I had to bet, I’d guess that the new iPhone will look something like a shrunken iPad with a rounded aluminum or glass back and almost nonexistent left and right bezels. OLED or not, it’ll have a 3.85-inch screen and a 300 PPI Retina display. We’ll get slightly better talk- and data-times, a 10MP iSight camera, and a VGA FaceTime shooter up front. No capacitive Home key, no NFC, no stereo speakers, no Nano SIM, and no (NO!) “static” haptics. Everything’ll be powered by a bigger battery, and the iPhone’s A5X brain will work with an entire gig of RAM to speed everything up. You’ll charge it with a normal 30-pin adapter, and it’ll come out in late September or early October.

And one more thing: The new iPhone will launch with iOS 6!

Duh.

[Lead image: fastcompany.com]