With Schiller's comments today about, “completely rethinking the Mac Pro”...
I wouldn't mind seeing this:
4+ Thunderbolt 3 ports
2 fullsized graphic cards
A 5k (or 8k), 38-inch Curved UltraWide Monitor with tiny bezel on the left & right side. Along with a Mac Pro that's powerful enough to run three of these side by side.
If Apple was going to go more outside of the box, maybe they'd create a more radical system like:
A small-ish box with an 8 core cpu, SSD, single graphics card, DDR5 ram, 32gb of Intel Optane memory, and 3+ Thunderbolt 3 ports. Cheaper than the cheapest Mac Pro model. If you want a more powerful model, you would just buy another one and daisy chain it with a thunderbolt 3 cable. It instantly recognizes the second mac with no setup and fully takes advantage of the second device. This setup would already be much more powerful than the current top of the line Mac Pro and would be about the same price.
If you are working with 8k video or rendering CGI or some other demanding work, you could daisy chain even more boxes.