Here's my wild prediction:
You pick a CPU module, a "base" module (w/the basic platform: mobo, power supply, 1 drive bay), one or more graphics card modules, extra storage modules, etc. You might even be able to click multiple machines together that with automatically configure themselves into a grid.
Ugh...sounds like a recipe to end up spending over $10k when all is said and done.
Here's what professionals need (regardless of the way Apple wants to believe they need):
Lots of RAM, and ideally lots of RAM slots so that we don't have to spend outrageous amounts of money to get us up to 64gb or more.
Powerful graphics cards, ideally CUDA capable, and multiples of them. Apps like Blackmagic Resolve can leverage multiple cards to offload the processing to.
Lots of crazy fast storage. TB technology is exciting, but also ridiculously expensive right now (with no real sign of coming down). Also, crowding your desk with lots of external stuff isn't particularly appealing IMHO.
FW is still alive and well...sorry! Many people with FW audio and video interfaces will lose their **** if Apple doesn't include at least 1 FW port in there.
Blu-Ray writeable...yup, shiny plastic disks are still a great way to deliver our work to clients, no optical drive also means no access to our existing libraries of stuff and old backups....not good.
Last but not least, we need a reasonable price for a number of reasons. Some of us with facilities need to purchase a number of machines and cost is definitely a factor. Secondly, technology is evolving rapidly, and we can't hold on to our workstations nearly as long as we used to, so the upgrade price shouldn't be crazy high.
A Mac Pro shouldn't appeal to the iPhone crowd, it's a machine specifically designed for a niche usage and it should reflect that. If Apple is thinking of giving me a glorified Mac Book Pro without a screen and call it a Mac Pro, they're not going to get my money regardless of how "cool" their new box looks!