The Mac Pro still has auxiliary power connectors, so you could theoretically install a GPU in it, just not the highest end ones. No drivers so you can't really do anything with them. I do suppose Nvidia could maybe do CUDA drivers for a card, but would Apple even allow it?
@paul they might let AMD, but I doubt they’ve gotten over their issues with NVIDIA
@sladewatkins @paul Craig did say during John Gruber’s event that Nvidia does a great job on AI and it isn’t something Apple is focused on. Sort of opens the door for Nvidia in non-Metal roles on the Mac…