First: Find the various GitHub mirrors of MediaWiki. Turn one into an up-to-date clone of our codebase.
Next, harder step: Make an interface to accept GitHub pull requests as merge requests in Gerrit, or do two-way syncing automatically via a bot.
Erik: "although I'm guessing that falls into the "hard" category, it could give us huge wins in terms of casual contribution.
Chad: "Yeah, that's definitely not straightforward--would need some careful thought to make sure we're doing it in a way that makes sense on our end too."