Wikipedia is currently under the GNU Free Documentation License (GFDL), a licence that causes incompatibility problems with the content also being released under Creative Commons licenses. At a party in San Francisco on Friday, Jimmmy Wales announced that the Wikimedia Foundation, the organisation behind Wikipedia, supports a solution created by the Free Software Foundation and Creative Commons to a long-standing problem: mixing CC-BY-SA content and GFDL is a no go.
It looks like what will happen is Wikipedia will version up to a new GFDL that will allow for integration with the CC-BY-SA licence.
Video and transcript of announcement here.
Wikimedia resolution on updating the licence here.