I don't see we even need an AC ruling. This is simple vandalism. We block vandals all the time.
I think this is precisely correct. Vandalism of Wikipedia is unauthorised and forbidden; blocks and reverts can be used freely; ISPs can be complained to, etc. An AC ban would serve no additional purpose, beyond making us feel good about our collective selves. In the unlikely event that Wik attempts to return and contribute in a bona fide manner, the AC can issue a year's ban, but otherwise there are other cases we should be looking at.
It would be nice if IPs of logged in edits were made public, as with logged out, as then individuals could take the initiative in contacting ISPs about abuse.
I've unprotected Wik's user and user talk pages, so we can have/link this discussion on Wikipedia proper, which will be good for keeping people informed. As and when the problem stops, they can be reverted and reprotected.
-Martin