While I don't really think 2012 will be that big of a change, I'll throw out a guess. Mine is for the 13", because that's the only size I care about.
Whatever processor is out from intel, I guess that's ivy bridge
Bump the stock ram to 1600MHz
Drop the SuperDrive
In it's place, put in a ~100GB blade ssd, move the standard HD there, and use leftover space to extend the logic board to be able to squeeze even a low end discrete graphics chip. While it would be nice to have two full-size 2.5" drives, a blade makes so much more sense. It would be nice if it was user replaceable but we know that won't happen.
With 1TB drives retailing for $100, the base price should come with the choice of a 5k1TB or a 7k750GB.
With the hard drove moved, extend the battery over the length of the laptop
Ditch the FireWire, in it's place a second thunder bolt.
USB 3 in place of the 2s
DO NOT remove the ethernet port, if they do they need to drop Pro from the name; it would just be a bloated Air
Keep the same form factor, but kill some of the screen bezel and shoehorn in a ~14" screen, there's enough room in the current model to do so
Offer a high res upgrade (1920x1200 would be BADASS, I'd jump on it even if was a $250 upgrade)
I guess offer a anti glare option, I don't really want it but there's no reason not to offer it.
Keep the body the same, there's no reason to change it. It doesn't need to be thinner, an doing so would only cause heat and space issues.
If they did so, I would be happy to pay $1500 for the entry level model, with $250 on top for the high res screen. He'll, even if the only change was a resolution bump to x1050 or better I would really have to think of picking one up, and just leaving my current 13" hooked up to my TV full time(I'm planning on buying a mini when they're refreshed but would much rather get a new MacBook).