I don't think Apple will even allow you to put third party video cards in this new Mac Pro (i.e. AMD), will they?
Right now in terms of official support they do not. There is zero eGPU support in macOS on M-series whereas it is supported on macOS on Intel. So there is currently a policy shift.
Is it technologically possible? Yes. Are they doing it now? no.
Are they planning to do it. It doesn't look like it. DriverKit has no abstraction for display GPU cards like the previous IOKit did. Some folks will hand wave that Apple is just going to do it all themselves in the kernel with zero 3rd party GPU vendor input. That is kind of dubious position. GPUs migh want to avoid DrierKits leveragin of iOMMUs, but Apple doing it all themselves is also a problem.
The major problem if Apple is doing this all in some super duper secret Area 51 laboratory with secret alien technology is that GPU driver tend to be like trying to balance a stick on a pin. When lots of different 3rd party applications get thrown at them bugs start to pop out of the 'woodwork'. Intel's dicrete GPU drivers have had massie problems. Even AMD 7000 series drivers seem to have a number of teething pains. Maximally hiding from just about everyone and stable drivers tends to be mutually exclusive.
It would have been far, far more useful for Apple to get out some extremely long 'beta' GPU driver iterations out on eGPUs for last year that they could iterate to being production ready in a reasonable amount of time closer to Mac Pro lunch. The more buried in the basement they have been the further they are going to be from being 'prime time' ready.
Adding to my previous point, the only reason why I still use a Mac is because it is a stable platform compared to Windows, and I've bought Mac-specific software, too.
In the past, Apple's GPU drivers have not particularly tried very had to chase every possible gaming hack possible to maximize frame rates. On Windows there have been "Pro" GPU drivers which tended to offer more stability and workstation app focused optimizations. And a more chaotic gaming focus drivers that consumer sector. Apple didn't have enough market share to follow two paths at the same time so mainly have followed characteristics of the "Pro" driver path on the Windows side. ( Also Apple's GPU tended to arrive closer to "Pro" card launches than consumer GPU launches. Coincidence? Maybe not ).
The problem with "it is going to be more stable" notion applied to macOS on M-series is that they done a whole lot of nothing. If they were trying to incrementally grow a stable driver solution they should have put it out there to get bug feedback by now. They could be doing things with heavyweight NDA's , but that isn't broad testing. Often those kinds of set ups just cherry pick the problem issues.
All the incremental improvement GPU driver and stability work over the last two years has been directed at Apple GPUs. Apple wants those to be rock solid stable even if they have to deprioritize everything else.