If user A gets blocked on wiki B, then edits wiki C logged-in from IP, that IP should be autoblocked when trying to edit wiki B.

While having global usernames has helped tremendously with tracking vandals, there are still a lot of tricks they can use in order to evade the block. Such a change would allow better control of blocked users for small wikis with no local checkusers (since stewards have conflicting rules over whether to do such checks or not)