I was talking to someone who brought up the interesting idea of per-user clones of the system that are mounted give the user total freedom to do things like install RPMs into their "user system" environment.
It essentially flips distrobox/toolbox on its head by using the running system as the base image rather than some arbitrary container image.
Can you do something like that already with systemd-nspawn? https://0pointer.net/blog/running-an-container-off-the-host-usr.html
systemd-nspawn
I think the idea would be to build on top of systemd-nspawn for this.