Yeah, to my knowledge, public development for any version of Fetish Master is close to nonexistent at the moment; I’ve been pushing to a couple different branches on and off for the last couple years, but I don’t think I’ve put together a release build for my version in over a year, much less released anything that actually takes advantage of the engine changes.
I’ve seen h.coder pop up once in a while in threads here or elsewhere regarding FM development, but either he doesn’t have time to work on it or he’s been keeping his work local. Maternal-Reads on Deviantart/Patreon has an overhaul mod of their own, but that’s mostly just gamedata rather than engine stuff and it’s mostly a private thing.
If you’re interested in doing your own work, my suggestion would be to to fork from hcoder’s repo, make your changes, and (once you’re sure everything’s working how you want it to), commit it and make a pull request from your fork to the main branch; if you want to submit it to be included in my fork, add my fork as an upstream and submit a pull request there too.
If your work only involves stuff in the gamedata folder (and not touching the Java source) I might still recommend releasing it as a mod anyways; both the main git repo and my fork are newer builds than what anyone else is practically using, and function significantly differently under the hood from the last full release of the game. That said, if you’re messing with the interface you’d realistically have to recompile and distribute the game jar, which would mean it’d be easier for everyone to have it merged into the official source.