I agree - I doubt anything will really change, long term, in the way admins use "back-channel" communications. They might at least pretend to be hard-asses about things like obscenities, ad-hominem bashing, and vulgar topics for the next few weeks though, I suppose... But really, how much fun is that? If people can't go into chatrooms with their wikifriends and type out line after line about furry porn for literally hours on end, what's the point of being involved with Wikipedia in the first place?
Of course, it's hard to control what goes on in IRC anyway - or more to the point, they can't just wipe the history like they can with good ol' MediaWiki. Once something gets said, that's it, it's out there, and the best they can do is claim that the logs were "fabricated," or that the offending conversation was "months ago, so it's no longer relevant."
Besides, all the really forward-thinking "cabal" members have been using IM for months now!