My thinking was that Lemmy instances could have their own Ibis instance that would include a page for each community named “c/community”.

While I doubt Fediverse wikis will replace Wikipedia, it can definitely take on wikis/fandom but, as mentioned, it can also act as the kind of wikis subs have. So you might have:

"c/community/faqs" "c/community/archive" "c/community/tutorials" "c/community/resources" "c/community/recommendations"

Depending on their needs - meme communities might not need much, while computing, privacy, etc might want quite a few to add in useful information and links that might otherwise get buried.