@Duncaen, the first two opts would be added to both utils anyway. And the third is all about making chown work inside uunshared jails (there are no such problems in case of uchroot). So if there's any other ways to fix it, I'd rather use them than touch user namespaces mechanics.
There are a lot of more things to consider to make chown work in (unpriviledged) xbps-uunshare. If you are ok with a priviledged tool just use xbps-chroot. IMO if you want general purpose container tool use one of the already existing ones.
> How would you change the hostname in a `chroot(2)`?
Will `sethostname()` not work after clone syscall (as I see from uchroot source code, UTS NS is also cloned)?
Generally no, I don't want to overbloat our xbps helpers, of course. Since fakeroot is very special case (which hovewer is made for working without root privileges), yep, let my third question be not quite correct.