Well, since doas has a Linux implementation, stealing that name would cause lots of issues to users who already use it or want to use doas instead of run0. This will be a default part of systemd; not a new package. The reason it’s called run0 is because it’s just a symbolic link to systemd-run, and instead of executing as an SUID binary, like sudo or doas, it runs using the current user’s UID.