Make an i5 15" with a nice screen resolution and switchable graphics for $1500 and I'll dump windows.
Then you aren't dumping Windows.
IF Apple were to up the res on the 15" they would probably go no higher than 1680*1050, otherwise there would be no need for the 17"
The Core i5 is basically inevitable, not sure if the next generation will have switchable graphics or not, and if they keep the low-end 15" then it won't be as cheap as $1500 and it won't have switchable graphics if the others do.
What you want almost certainly will not happen. If you need to put constraints on your switching (If Apple sold a $500 headless Mac with a Quad Core, 4 hard drive bays, a bluray drive, and upgradeable graphics then I would switch) then you aren't switching. Which is fine, 7 is a great OS, and I am sure somewhere out there are nice PC laptops.