This reminds me that the issue of wanting to customize the UI based on the users membership in groups has come up in various forms before (can’t find too many topics though, so maybe it was just in my head). For example:
And then there is, of course, the “Click me” button plugin:
In more general terms, this means that on certain forums groups distinguish quite different user groups (esp. on those forums where setting up different discourse instances was an option). So the question occurs to me whether it would not be possible to make it so that certain CSS classes can be hidden or shown based on a user’s group membership, i.e. to allow site owners to customize their sites appearance for different users via CSS.