Feature summary:
Change Special:MassMessage so it also allows targeting specific user right groups like admins, active reviewers, bots, etc.

Use case(s):
Admin in SqWiki. We'd like to be able to send talk page messages to all the active reviewers or all the (active) admins periodically. Categories can be utilized for that but in small wikis those are far from perfect and can be unmaintained. Special pages Special:ListUsers and Special:ActiveUsers are failproof so we'd like to be able to automatically query results from there in Special:MassMessage. That would also help excluding certain groups from the results, like bots, if so needed. Other solutions are also welcome.