Desktop 4 with PCI 3.0 cards

If the next attractive CUDA GPUs from Nvidia are designed for PCI 3.0, I would consider looking for a workstation that would take advantage of that. I currently have a GPU Xpander Desktop 4 - any ideas on how that would interact with PCI 3.0 hardware? I know this is mostly an academic question since those products are not quite on the market, but I'm curious where the bottlenecks would be in such a set-up. I currently have 3 GTX 285 cards in there for a DaVinci Resolve on Mac Pro set-up.

Cheers,

KC