I finally got my wiki project polished enough for release and posted the announcement last night. I read the Gemini spec for the first time in late May. The question of a suitable user interface for editing text over Gemini was bubbling in my mind since then, and I think I came up with using sed commands in early June.
Announcement message on the Gemini mailing list
[HTTPS] twinwiki project page on Sourcehut
I'm pretty happy with the wiki implementation. Granted, it's more a proof of concept than a finished piece of software. But it's Rust so there won't be many unexpected crashes, and the architecture should be good enough even for Wikipedia-like frequency of edits. Not sure about the database (sled), though. I'd use PostgreSQL if I was serious, but I wanted to try a pure-Rust solution with an embedded DB.
Twinwiki is the first Gemini native wiki as far as I know. Alex Schroeder was already using a wiki that serves pages over Gemini and is edited with Titan, a companion protocol. I learned about it a couple of days before my announcement. Alex's wiki is probably significantly easier to edit and more featureful, but I'm not sure if the source has been published. Also, I personally prefer working with just Gemini itself, trying to expand the boundaries of what's possible with a simple protocol.
I guess that's all for now. Feedback, comments and contributions are welcome!