How about this for a draft license:
Wikimedia license 1.0
Preamble, this only exists to give us an escape route if need be
1. Anything distributed under this license must conform to the terms and conditions of the CC-Wiki license or the GFDL license or the CC-BY-SA license.
2. Anything licensed under this license will also be licensed under any later version of this license.
------ If we put that into lawyer language, then we don't really have a proper license, but have the ability to add in another clause in a later version saying "and it must confom to the terms of the foo-licnese". Hence the wikimedia foundation can in effect add a new licnese which which will be backwards compatable when ever the need may come up.
i dont know if this is actually legaly possible, but it might be worth a shot.
paz y amor, -rjs