The thing about NVIDIA support is that it was never officially there in the first place, almost everything has been a hack/workaround by the egpu.io community. At the same time, Apple has been countering with increased security in the form of the T2 chip. What Apple didn't need to do IMO was refuse to support older OSs on machines that contained the T2 chip whilst simultaneously refusing to approve NVIDIA's drivers for Mojave/Catalina.
This last point is critical - if you buy a machine today with a relatively small hardware change like the T2 chip, you are obliged to use Mojave/Catalina by Apple. You cannot install HS on a Mac with a T2 chip. So Apple has form here.
So when @CYOA says:
Are developers going to have to rewrite software and roll out buggy updates to adapt?
There's a pretty good chance that it just won't be possible to simply roll out a patch for many applications because it's not only a HW but also an OS change and crucially it's about the new way in which the OS uses the new HW. So a major HW change like a new CPU architecture is, IMO, quite likely to be problematic for many software applications, and not just for the obvious reasons.
Personally I wouldn't buy a new model MBP within the first 6 months of release because all the fanboi noise makes it hard to objectively evaluate any major issues like this...