"make -j" has OOMd me more than it's worth. If it's a big project I just put in how many threads I want. I do hear your point but that is a solved problem.

actually, global jobserver is another unsolved thing that seems unvelievable nobody has done yet. You have server. Server spins N containers (kubes, dockers, multiple user sessions ...), each of them is building something. There is no mechanism to run batch of tasks in parallel in a way that uses available cores. Some special cases (make/ninja/gcc) work, but no general mechanism I know of