to me it is very important that the machine I invest in is at least capable (if i need to) run another operating system... w32xx is a 2 year old platform, and apple can’t do nothing to prevent us to upgrade in the future if we want to. the 2021 mac pro will probably just gain pcie 4.0 speed and call it a day... appart from the 2013 trashcan macpro generation always had a real hardware upgrade only every two generation 1.1 can be flashed to 2.1, duno about 3.1 because at this time intel had the same socket for ever, and then 4.1 could be flashed to 5.1....
From a industrial standpoint the 7.1 chassis is not going anywhere anytime soon, and I am almost sure that the 8,1, will have the new xeon 10nm and pcie 4.0 just by minor hardware changes, and probably just a firmware update. they don’t sale enough machines to totally overhaul the 7,1.
vega20 is pcie 4.0 compatible, and i am quite sure that the mobo is gen 4 compatible... as soon as you drop a new 2021 xeon in that support pcie it will be compatible... the only change is that they will probably be able to lock cpu upgrade via firmware and the t2 chip... or they will just change the plx and t2 chip to pcie4.
I own a 7.1 and sure there’s a lot of pc out there more powerful for 1/3 of the price... but none cant run 2 massive gpu , 4xm2 ssd , 8x2,5 »ssd, a raid card and a black magic 8k capture card at the same time flawlessly and without making any noise.
There is no upgrade path for the current 7.1 Mac Pro, Intel is not making any new Xeons for the socket on the mobo...