Walked around Fusion Festival with Bitchat running. Saw about 20 other devices and a few messages. Nobody replied to my messages. So usage isn't zero, but 20 devices out of 80000 people isn't a lot. Most hops I saw was 2, meaning there wasn't enough density to make it any meaningful distance across the festival grounds.
As far as I'm concerned, it was used at several protest and is currently in use in Indian CJP protests. Also Indian government made a request to take down it's repo on GitHub
That's already a lot for such a niche project.
Many CCCers attend Fusion.