This does not sound promising for the future of the Mac Pro but all we have at this point are rumors. Every single new Apple Silicon device that replaced an Intel device has been a huge step up in every way. Will Apple really let their flagship Mac be the one device that’s actually a downgrade with Apple Silicon? I don’t think so.
Personally I think the Mac Pro will use a modified version of the M2 Ultra perhaps with a few extra cores. Maybe this modified version will allow users to upgrade their RAM for system memory while the internal unified RAM is reserved for GPU task. For an extra power bump, Apple could create their own GPU that can plug in and work with the built in M2 Ultra to add additional GPU grunt. From there Apple could make their newer chips (M3 ultra, M4 ultra, etc) available to purchase as a standalone unit that can be installed in the Mac Pro chassis to upgrade to the latest CPU. I believe there were rumors last year about Apple modifying their silicon for use with the Mac Pro so maybe this is a possibility.
I just can’t see them releasing another Trash Can like, locked down Mac Pro, right after releasing such a customizable Mac Pro. It’s already bad enough that they are apparently using the same design…