That’s a scary prospect for people who’ve shelled out so much for a Mac Pro. Alternate (and perhaps hopeful) future would be for Apple to retain the Mac Pro as an ARM device but write the drivers necessary for GPU upgrades. That would give hope to those of us who use eGPUs for Boot Camp gaming.
Apple most likely won't work with nVidia again at this point. Seems like they burned that bridge a long time ago.
They "may" work with AMD to provide ARM versions of their drivers, but... I'm not hopeful because AMD can barely write "workable" graphics drivers for x86 as is, and they barely update their drivers on the Mac, if at all.
Due to that, I think it's highly likely that Apple will just drop support for eGPUs and modular GPUs altogether.
Also there's no Boot Camp anymore (confirmed at least twice), so there's no point to having these GPUs for gaming.
Their message is clear: if you need Boot Camp, their Mac platform is not for you. If you need a modular Mac that can take components other than what Apple provides, the Mac is not for you.
They're plugging up all of the holes and making sure the "walled garden" becomes even more "walled up". While some may like that, I'm watching very closely how it all plays out by the end of the year. Likely, what'll happen is I'll probably just own a "whatever" MacBook that barely does what I need, and then I'll have a Windows computer on the side for heavy lifting. And that'll be true for the next 10 years.
I really was going to pull the trigger on a Mac Pro but after this WWDC, Apple has effectively killed off the idea of me ever owning a Mac Pro at all. As a potential Mac Pro owner, I'd say what Apple announced was no less than a slap in the face.