I remember a time, in ancient internet history, I was using an app call Trillian and later Pigin (open source equivalent), both were able to connect to many if not all existing messaging protocole and bring all your chat in one place, with one unique UI.

Matrix did build something like this with bridges, it didn't really took off as far as I know.

But the idea was always appealing, you use one new decentralized protocole, like here with nostr relay, but also offer to connect to Signal, Threema, Telegram, Simple X, ... open source messager protocols. So you can start using it right away, and convert people easier as they keep their network and use it from day one as well.

I understand the complexity would be demultiply but it could start with a fork of Molly, add nostr relay as a second network, backed in ecash and start from here.