Comment 1 for bug 2045768

I don't have time to provide a fully researched answer, but I hope this will help.

If you're not already familiar, I suggest you start at https://www.debian.org/doc/debian-policy/ch-opersys.html#users-and-groups. Ubuntu cannot allocate these without potential future collision with Debian. So you should ask Debian in the first instance.

I'm pretty sure I speak for Ubuntu developers when I say that this cannot be considered for Ubuntu alone without a discussion in Debian first.