Here's the thing, Nix is to slow (even ignoring `nix-env`'s terrible search functionality which should just be removed). What that requires is some good old boring profiling and optimization work. If he were to contribute that to a distro/package manager that basically shares his vision, this would be much more useful to the world.
Cause, at the end of the day, the work isn't so much maintaining the package manager as maintaining the packages. That's simply too much work for anyone to do alone.
http://blog.williammanley.net/2020/05/25/unlock-software-fre... is good piece on why the ultimate issues with packaging are social, not technological. At this point, when the vast majority of devs don't seem to act as if there is a commons that even needs integration, I don't think any 1-person technological solution is going to be so good as to upend the social situation.