Emanuelle, I don't see how this would be generally useful, but what's even worse I don't see how this could easily be implemented without adding a database call into the (hypothetic) user_display::get_name which would get executed for each returned name when assembling a list of names.
But I think the initial thought behind the numbering scheme was that sites could insert their custom privacy levels if they wanted to, and if the display proc would be nicely centralised then that would be easy.
Apart from that - what level of group/subgroup membership do you mean? All users of a site are part of the same group - Registered Users - for example, which would make the privacy level useless.
