I suppose it's possible that somewhere, Apple is writing drivers for AMD or Nvidia's cards.
As mentioned in the article, the 2019 Mac Pro has updated GPU offerings, including the RDNA2 range. AMD will certainly still be under contract to maintain drivers for their GPUs, under OS X. So, the obvious solution would be for AMD to provide dGPUs for the new Mac Pro, also.
What's sort of interesting is that AMD
would have to port its drivers to ARM. However, AMD drivers on Linux will work on both ARM, POWER, RISC-V, and other CPU ISAs.
So, I wonder if this will mean that the new Mac actually has
less RAM than the max configuration of the 2019 model. Does anyone know? That would seem to be an issue, for some.
Dropping down to the implementation details, it seems almost certain that Apple will have to implement an external PCIe switch, in order to support SSDs + PCIe-based peripherals. I doubt the M2 Ultra would have anywhere near enough lanes, especially if they were planning another version that's 2x as large!