The wiki is mostly dead, its data mostly useless. Whatever we'll build as its replacement can start with a new, clear license system, and wiki content is either relicensed by its author and then ported over or deleted/rewritten.
I'd go with CC-BY for the simple reason that documentation acts as marketing material which should see the widest distribution possible. People who dislike licensing their content that freely can publish elsewhere and set up a (CC-BY'd) link.
In any case, we can (and IMHO should) decouple the discussions about dealing with current content and about future licensing.
Patrick