I'd like to see a replacement for MediaWiki, even if it doesn't support as many features. Our online documentation is mostly written by the community in the wiki, and it would be nice if we could consolidate the wiki together with the forum/blog/profile system. Migration isn't even that big of an issue, since it is easy to copy and paste an article.
All it needs is articles any authorized user group can edit. I'd make it simple in structure and just let the users define the layout of the articles.