I don't think they'll take away the expandability of the Mac Pro since that's pretty much its only unique feature.I'm curious about whether the new Mac Pro will lose all PCIe slots. Plus what the RAM limits will be. Currently it can have up to 1.5TB. I'd hate to think how much that would cost if it is all soldered to the CPU.
They already did it once with the trashcan. They ditched the design supposedly because of thermal problems with newer CPU and GPU. So, I wouldn't put anything past them. The low thermals of Apple Silicone would allow for something G4 Cube or Trashcan Mac Pro size. With the specs they are talking about. I think a lot depends on whether Apple intends to build a discrete GPU card.I don't think they'll take away the expandability of the Mac Pro since that's pretty much its only unique feature.
Besides, I'm sure they'll find a way to sell upgrades with that lovely Apple Tax.