This seems quite possible.
Incredibly unlikely, other than the fact I've yet to see proof of their being 900 shaders, just a REALLY bad picture that shows 8 rows of identical parts on a electron microscope picture of the core, and deciding another row next to it has to be more shaders, and Anand making the point that when you go really small you DON'T need redundancy but because they said the word thats all people focused on, basically, i highly doubt it has 900 shaders.
But, a new process is ALWAYS< ALWAYS without question lower yield, so if they can't release a 900 shader part now(if infact there were such a possibility) then theres no way they could do that on a new core.
Die shrunk 1000 sp's, few more TMU's/rop's etc to compensate and probably clocked up towards 900, maybe even 100Mhz, maybe an extra 200-400Mhz on the memory if its doing well at the moment though they might keep that the same who knows.
Nvidia, every chance their 40nm is doing well but no rumours of them taping out at all, no sign of anything meaning probably their ridiculous delay to 55nm, and ridiculously clinging to this part when it was so late seems to have leaked over to delays on their 40nm part.
As for the idea they'll just wait for the next gen 5XXX part end of year, its highly unlikely, why, because they've always liked to test a new die size on a relatively easy shrink with relatively few changes and have it tweaked and ready for super high yields on larger newer more complex cores. Not to mention TSMC WILL have 40nm available and theirs more profit to be found after a month or two on a new process, so for 4/5 months they'll make more money by switching to 40nm asap.