This is something I’ve had an eye on for a while - for mobile and non-electron desktop usage ;). I have two main efforts on the go:
First is a libpurple plugin. In principle, this can be used with pidgin, or with chatty, for desktop or librem 5 phones. However, deltachat links against openssl, which is a no-no with libpurple, so you can’t distribute the binaries. OpenSSL v3.0.0 will solve this - I’m unlikely to do anything more with it until then, or later, but the status of this last time I touched it was that you could send and receive messages.
Second, is a telepathy connection manager - this is a new project and isn’t functional yet. No licensing issues, however . Telepathy means it can work with Empathy, KDE Telepathy, maemo leste (probably?), plasma mobile… I’m not sure what proportion of linux phones use telepathy, but I think it’s at least a few.
Completing it means I can turn my pinephone into my daily driver, so I’m a bit motivated, but battling my own ignorance in a number of areas simultaneously with this one, since it’s written in rust and is pretty close to the (dbus) wire.