From Consumerium development wiki R&D Wiki

    Its texts default to the GFDL text corpus but authors can decide to use, or can quote, Creative Commons texts or other free documentation as well.

    How does this work out in practice. I suppose that if an article consists of GFDL'd and CC texts it is not applicable to maintain the texts discrete of each other thus resulting in CC texts being subliminated into GFDL, which AFIK is a violation of both licenses
    Probably true. But no one knows, because, it's too new.
    Also, the GFDL as applied to a large public wiki is held by some to be almost equivalent to public domain since there is no way to make a case against copyright co-owners, and no practical way to get permission from all involved parties to pursue a case of copyright infringement. There are many specific critiques of how stupidly Wikimedia has mismanaged this, go read it on the wikilegal list which should be called stupidsysops list.