What you need is an Eclipse Foundation like setup where large corporations/system integrators make money on complementary services and therefore can afford "altruistic" contributions to a real open-source project like MediaWiki. Well, not only "afford" but
"have to". :-)
As much as I support open source concepts I have to admit that most of it remains untested in the courts. Patents can be a bigger problem than copyrights because they cover the ideas rather than just the expression of the idea. The first person to the patent office has an advantage even over others who may have had the idea earlier.
That's why you need a proper setup. The Eclipse Foundation, for example, requires signing away any claims based on patents used in source code contributions before they get accepted. It should be the same for MediaWiki and related contributions.
Dirk