Well, it might not belong in its present form—but, since they're compatible and cite each other fairly frequently, it'd be nice if the entirety of other encyclopedias could exist "attached" to Wikipedia somehow, so that any archival efforts going into Wikipedia would bring them along as well. Since wikis are usually "flat" namespaces, perhaps as subgraphs (that is, subdirectories)?

There are so many wikis that are basically "Wikipedia, but for this particular topic that on its own isn't notable enough"—if these could all be merged into Wikipedia this way, the ecosystems of both Wikipedia and its offshoots would probably be a lot better off. The members of each wouldn't be tending only their own own walled gardens, but rather crosslinking and cross-editing more heavily—and putting things where they really belong, instead of trying to justify their inclusion into their own project of residence!

They wouldn't even need to exist "within" wikipedia physically; perhaps Mediawiki could adopt something that works for articles like Trackbacks work for blogs, where all articles from all "public encyclopaedia of [topic] project" Mediawikis show up in one another's indexes?