Yeah. I'm definitely for some pretty seamless integration. Probably in the optimal case:

• The wikis would be hosted on the same domain as the Lemmy servers.
• Any account you had on the associated Lemmy server would automatically exist to the wiki as well.
• If you were logged into Lemmy, you'd also be logged into the wiki.
• Only mods would be able to enable wikis but the process of doing so would be trivially easy.
• I'd personally say that it makes the most sense to just have the mods link the associated wiki from the sidebar rather than creating new special interface features to add a link outside the sidebar or whatever. (Unless some kind of plugin infrastructure that would allow that already exists.)

But all that can be done without putting any wiki-specific code into the Lemmy or Lemmy-UI source repositories, which I think is preferable for the same reason you wouldn't add flight simulator code to a spreadsheet application. (Ok, maybe a bad example, but you get my point.)

Edit: And I'll admit there are both upsides and downsides to my approach here. One downside would be that some Lemmy instances would offer attached wikis and others wouldn't. It's possible it also just wouldn't catch on at all and nobody would enable attached wikis as a feature if it was a whole separate step to setting up "Lemmy".