'it can't be done' must be your motto
Haaaa ha haa haaa ha haaaa haaaaa, oh stop, haaa ha, please no more, ha haaa ha hhhhaaaa ha ha. I always try to be nice, but this is plain idiotic.
Oh MikeDTyke, let's do some basic math. I'm going to just use one figure so we don't have to do this twice, and say the new device would have battery capacity 2.5x that of iPhone.
Features where screen size would draw extra power (say 50% more), you take the previous figure, less 50% in screen drain, times 2.5 more battery capacity:
Internet use:
Up to 5 hours on 3G : (5-50%)*2.5= 6.25hrs
Up to 9 hours on Wi-Fi : (9-50%)*2.5= 11.25hrs
Video playback: Up to 10 hours : (10-50%)*2.5= 12.5hrs
Features where screen is irrelevant:
Talk time:
Up to 12 hours on 2G : 12*2.5= 30hrs
Up to 5 hours on 3G : 5*2.5= 12.5hrs
Standby time: Up to 300 hours : 300*2.5= 750hrs!
Audio playback: Up to 30 hours : 30*2.5= 75hrs!
None of these features require any extra processing power, so 3 unused cores could be shut down. Apps like word processing and spreadsheets take even less power than surfing the 'net. When you want to do heavier duty processing like iPhoto, iMovie or GarageBand, you're likely going to have it docked anyway - touch is great, and complimentary, but doesn't replace a good keyboard & mouse.
As for your response about applications, Apple has already brought multi-touch to MacOS, they just don't make any Macs with a touch screen, yet. The only trick left here is to get apps to run on ARM.
Don't count Rosetta out - people never thought something like it would be possible in the first place. And as for LLVM, that in conjunction with GCD has provided Apple with a good INCREASE in performance.
Now, you did notice that I said developers would have to recompile, and release a new version to something like the App Store, right? One would presume you'd have to buy a new copy.
Companies the likes of MS & Adobe were told to get their butts on XCode 8 years ago. Not Apple's problem if they didn't listen. Another developer will come along and fill the gap. Case in point - I no longer use Photoshop, instead I've switched to Pixelmator, which has all the features I've ever needed from Photoshop, and runs better.
The iPhone platform already runs MacOS X, Apple has just left a lot of features out. They need to port the rest of it over for the tablet. Developers would need to port apps (or write new ones) just like they have done for iPhone/Touch.