I also don't get this sentiment with 3:2 screens. I think that there's a 99% chance the new screen will be 1152 x 640 @ 4" because it just makes sense (no scaling for current apps, perfect scaling for expandability, allows for virtual buttons so home button can go with the DODO). As a developer, I would rather see a 4" 1152 x 640 screen than a 4" screen with 3:2 aspect ratio. It makes absolutely no sense to make something that has such an arbitrary scaling ratio (which kills performance), and it also makes no sense that all user interface elements have to be scaled down because the screen is physically bigger.
Also, I think A5X or A6 is quite a stretch at this point. I'd realistically say it'll be an A5 with 32nm, just because there is no need for Apple to scale up their processors even with a new screen factored in, and they'll need the extra power consumption headroom if they want to implement 4G/LTE. But I think 1GB RAM is quite a possibility, and who knows, they may end up calling it an A5X with 2 GPU cores disabled.
I'd also guess that they'll stuff a bigger battery in there even if the enclosure is the same size or thinner. Seems like the 4G/LTE radio will be the monster drainer there, and they must absolutely have the battery capacity to counter that. Especially if they don't want the device to crap out on tethering.