Not having the latest OS isn't the end of the road either.......
Supported or not, I am still using my cMP with Mojave.
True. This is also a testament to the expandability of the system that has given it a longevity that their other systems don't have.
If one is considering at a system like the 7,1, then most likely it is because of a work purpose that is served by more than just sheer computing power. Upgradeable components, far greater expansion, the best cooling for sustained workloads, etc are other things that are of appeal. Ironically the closed system of the 6,1 is in part what doomed it. And the 5,1 has had such a community and longevity simply because of its expandability.
One could argue that Apple silicon changes the game in regards to speed, power in a far more favorable thermal envelope. But if the new 8,1 is indeed a "closed" system like the 6,1, it will follow in the same footsteps as the 6,1. Simply because whatever power this new machine brings doesn't live in a vacuum... the whole Apple eco system will exist on its own silicon too. So as new MBPs and iMacs and Studios come out with better SOCs for less money, people will complain that their Mac Pros can't be upgraded to better last. Hopefully they include some PCIe expansion to at least serve its intended market better like the 7,1.