I don't think it's feasible either, just wanted some comments(even the guy who posted this originally says it's just speculation)

But it should have:
512-bit bus, ATI has it, it's faster, newer games need the memory bandwidth for :
1GB GDDR4 RAM, i have no doubt they could make it with GDDR5, but they're doing well on the price/performance front right now, i really hope it'll keep up.
200+ shaders, it needs a serious boost in power, Crysis etc. 8800GTX held the crown for over a year, the new one should do it too.
And in regards to the TDP, the 45nm tests that have been out so far in regards to the Penryn processors really show that you can clock them higher than ever before, while still using a very small amount of power.
And also, they have to support DX10.1, anything else would be stupid.