I think the concept of hydra is good. I currently own a 9600GT, and I'm planning to upgrade to a new ATI/AMD card this year, and being able to keep my old card in the machine as an extra boost or even just to handle PhysX would be nice. This however brings up the question of how does hydra deal with drivers? Does it have it's own to handle both cards or what? Would it be possible to have my old nvidia card dealing with PhysX or will it be the same fiasco we have now if we try to do that with an ATI card in the main slot?
hydra i beleive will use its own drivers to make the cards work together. i expect poor infrequent driver support for this and its likely that the cards would be slower than using ATI or nivida drivers.