Worst case scenario, upscale gaming stays on PC as is the case with many global markets.
As much as I like the PS3, it is very similar to a PC in all aspects other than basic PC functions like user interface and productivity software. I still prefer the use of the PS3 as a media center, even directly compared to WMC because it operates like a set top box with the remote. I have a media center PC with integrated remote and TV functions and it's still not the same in terms of convenience.
The 360 is pretty redundant if you have a gaming PC and are not playing on XBL.
I think it's still way too early to say either is on the endangered species list though.