Mac Pro as we know was always financed by the volume of workstations and servers sold by Intel, Apple always iterated and tweaked on the reference designs provided and already payed for by Intel selling tens of millions of server CPUs. Now Apple have to finance (as in ROI) everything itself.You are assuming that the Apple SoC used in the upcoming Mac Pro will be similar to the M1 or M2?
Pro users won't go for that, we want PCI-E slots and upgradable memory, Apple learned it's mistakes with the 2013 Mac Pro. Tho the Mac Studio maybe Apple's way of testing the waters on never releasing the Apple SoC Mac Pro.
Pro towers like the 2019 Mac Pro don't sell in large numbers, Apple may just cut us loose.
Apple investment with Apple Silicon to this day is completely focused on that Apple can sell high volume, as in millions of units - like iOS devices, MacBook Airs, MacBook Pros and some devices that have less volume but are really needed to make a complete line of products and not to difficult to implement with the current chip designs, like the 24" iMac, Mac mini (exactly the same M1 CPU of Air/13" MBP) and Mac Studio (same or doubling the M1 Max CPU design of 14" and 16" MBPs). Apple don't even have a 27" iMac substitute to this day, almost two years down the road of Apple Silicon.
If you are taking clues from the current silicon designs and how Apple is implementing the support software, you can easily see for yourself that RAM and CPU upgrades are not even possible with the M1 and M2 architecture, unless is something along the lines of a much slower level 2 RAM buffer or or a full CPU on a card/module that is removable, that you will have replace the full card/module when upgrading - something that I really don't think that Apple will do, but it's possible.
Apple will have to change radically the M2 design to reimplement the 2019 Mac Pro with Apple Silicon, which I really doubt it since even if you account the number of Mac Pro ever sold to this day wouldn't have a return of investment necessary. The most probable is that we will get something like a doubled Mac Studio Ultra on steroids, with new I/O and slots for additional network/audio/storage cards but not upgradeable RAM or CPU.