It would be really nice to see two kind of groups (or categories) introduced in q2a:
admin set groups: when registered user is subscribed to these groups and see questions from these groups on his frontpage
user created groups: if user will reach certain points, he will be self-promoted to admin-set user group which have abilities to create groups, other users need to subscribe to these groups and see questions from that group on their frontpage.
group starter can also set role or points required to publish questions in his created group.
also users might vote for group itself