What chance is there that MediaWiki will *ever* be useful for this purpose? Its developers are only interested in Wikipedia, and in increasing the power of their sysop power structure by adding on a permission-based model no one really needs, but which makes them feel powerful.
They haven't even cloned the GetWiki facility yet, and it's the ideal way to keep those who fork off the GFDL corpus as close to the core corpus as possible. That is of course because they are trying to stop all other GFDL corpus access providers, and retain trademark power over the name "wikipedia", which is actually generic. There are many wikipedias, and the contributor is not seeking to enable or give their work to any specific bunch of "Wikimedia" thugs, they're seeking to give it to all wikipedias.