A couple points:
- 2K
is 1080p, ie 1920x1080. 2K can also be a few other similar resolutions, up to 2560x1600 in 16:10 aspect ratio, though people tend to use the specific resolution or name for the sake of clarity in such situations.
http://en.wikipedia.org/wiki/2K_(resolution)
- Lots of phones are already up to near 500ppi, so I see no issue with Apple doing this if they want to.
- aspect ratio is not important for preventing fragmentation. Resolution is. Till now, app developers have to scale their programs based on a multiple of 568x320 to get the apps to scale to the iPhone 5/5S screens. Going to 1080p means a non-integer multiple of the base resolution, which means fragmentation.
- Apple will want to avoid fragmentation, or else they are no different from Android. Right now Apple is supporting 960x640 and 1136x640, and with 1080p for one of the new iPhones 6's, it will be a third resolution, and with another different resolution for the other iPhone 6, yet another. Apple will not want to have 4 separate resolutions for their different iPhones.
- whatever they do I think the two iPhone 6s will have the same resolution. Maybe not 2272x1280, but not two different ones.
- For apps to scale cleanly to all devices (except the iPhone 4/4S) 2272x1280 is the only option that scales with minimal effort, simply by doubling the resolution in each direction. In that case, all future apps could be written with a base resolution of 1136x640 and scale up from there, giving app developers more freedom and a lot more pixels to play with.
- If Apple really comes out with 2 sizes of iPhone 6, then another solution, though a little messier, would be for the 4.7 inch to be 1704x960 at 416ppi while the 5.5 or 5.7 inch will have 2272x1280 at around 450-470ppi.
- The A8 chip, hopefully with more RAM, will handle any of these resolutions with absolute ease. Computational power and battery life will not be a concern, given the incredible power of the A7 already. The A8 will be further optimized to reduce battery drain. And a larger phone will have a larger battery which will more than make up for the larger screen.
I can't see Apple not competing with other great screens out there now that they are probably moving to a new screen size and have a chance to do something great. Hopefully they will.