I guess what I was thinking of in Receiver-side Cutoff is just IRC without bouncers. People can’t continue sending when you’re not connected. Seems like a good idea. Also no GDPR/DSGVO problems, because messages aren’t saved.
Hackint has a web client that is fairly useable. You can link directly to a channel by changing the URL. For mobile use, you can open the URL once in the browser, then use “Add to home screen” to make it feel like an app. Seems simple enough to me 🤷
[Update 20230303:] After some bouncing of ideas, I’ll be available in the moderated channel #stammtisch on hackint.