it is indeed a fantastic idea, which I was also thinking about in the last two years during my time at SOAS in London. Even though every student uses Wikipedia, actually contributing to it regularly and taking part in events or administrator work has a geeky sound to it according to most and this is one of the reasons, from my personal experience, that Wikimedia Societies don't work well at most universities. Sad.
There are several geeky societies at my Uni that seem to cope fine. They form an ad hoc alliance together against the rest of the world where needed too, called GeekSoc! (We managed to double or even triple the usual turnout to Student Union meetings when one of the societies was threatened - a force to be reckoned with!) I could probably organise a Wikimedia Soc, book a computer room in the library one evening a week or something, see what happens... Someone remind me once term starts again (October for me)!