You bring up a lot of good points.
But I would just like to point out that our 5.18.5 plasma and 3.36 gnome which we released with 20.09 still have many rough edges. Even a week after releasing, I’m still largely doing, “damage control”.
The point I’m trying to make is, we would still be in much better of a state than we were with the early September branch off.
Although there still hasn’t been any 5.20 plasma development on master; if we “get things rolling” with a well-structured project/issue (similar to Convert remaining python2 applications over to python3 · Issue #101964 · NixOS/nixpkgs · GitHub), and maybe a special branch+ hydra job, then it “easier” to distribute the load with the community.