Another idea: “stories” app
You know, like Instagram, WhatsApp, now Telegram, Signal.
Though I think it’s not really going to be as capable and useful as built-in stories can be because you rarely have a group chat that has all the people that you would like to see your story. E.g. you don’t have a group chat that has your school friends and university friends together.
Which is making me think of per-account instead of per-chat webxdc apps
Update 2024-01-01: In addition to @adbenitez’s idea of a mailing list (below), it would also be fun to add people to such mailing lists with an invite link (which, unfortunately, is not possible (yet?)), which you could post to your profile’s bio, similar to how Telegram does it with its “personal channel” link.