I asked this same question few time ago, even on IRC and they resent the mail to the Communications Committee of the WMF. Here's the answer I got:
Mike Godwin wrote:
Assuming I understand the question correctly, any currently compatible wiki could adopt the new GFDL/CC harmonized license within the time window specified by FSF.
--Mike
On Jan 3, 2009, at 10:30 AM, Mark Pellegrini wrote:
Today in IRC, Isaac Barrera from Astronomipedia (I am cc'ing him on this email) came into IRC and asked an important question. With the new escape clause in the GFDL and possible relicensing of WMF projects, he asked what Wikipedia-compatible 3rd-party wikis should do to stay compatible with Wikipedia. This is information that should be posted prominently on the WMF website.
-Mark
But I don't think it's clear enough.
El mar, 10-03-2009 a las 14:08 -0600, Chris Watkins escribió:
Should a non-WMF project go for dual-licensing? I know this is a Wikimedia Foundation list, but the clarifications needed here will be helpful to Wikimedia people as well.
Specifically, I'm trying to understand whether there is a significant downside to dual-licensing - comments by Erik and others suggest there is, and this option is only being pursued as it was part of the agreement with FSF. I'm not clear why - this looks to me like an elegant solution that gives more freedom to the people re-using the content.
My question in full is here (but it seems to be a quiet page):
http://meta.wikimedia.org/wiki/Talk:Licensing_update/Questions_and_Answers#S...
Thanks.