SchmidtIT, or something, released a bridge just to share users a long time ago, but it doesn't work with the latest version of MediaWiki.
XenCarta is way too simple for what I want to do. It's basically a way to allow users to create static content, rather than a wiki.
VaultWiki is a lot closer, but it lacks a lot of the syntax parsing I need, and (since it's not actually MediaWiki), I can't use add-ons for it. I also could not find a way to move discussion off the same page as the content and that's basically a deal breaker.
I'm tempted to start up a bounty for this, since what I want seems so simple, but would require time I don't feel like putting into it. I don't really know XenForo well enough to not take weeks upon weeks to figure it out.