Performance level GPU pooling isn’t possible at this point for real-time graphics rendering and gaming. Virtualization of GPUs to smaller instances is just taking off. Possible in the future we will have transparent pooled virtual GPUs. Right now we can’t even get SLI working properly and transparently with GPUs connected directly next to each other.
Another concern for me though is them partnering with Havok. Correct me if I am wrong, but PhysX is the only physics API that is allowed to use GPU acceleration (I think Nvidia has the patent). However, they recently opened up the PhysX API to be used with AMD hardware as well and it is no longer proprietary to Nvidia GPUs. So, why aren't they using PhysX with Stadia? Imagine distributed computing with GPUs accelerating the physics...
Havok has turn-key optimizations for AVX v2 from Intel.