Maybe I'm not understanding, but it's pretty easy to edit the wiki from the command line in vim (I've used text editors for it before).
https://fossil-scm.org/home/help?cmd=wiki
To edit a page, do an export and then a commit when you're done. It was easy enough to add this as a menu item in Emacs.
fossil wiki export foo.wiki foo.md
fossil wiki commit foo.wiki foo.md