That is everyone's dream. The problem is every startup/project with $$$$ is investing into reinventing the entire client/server wheel (Signal, Wire, matrix, threema, etc..) instead of investing their $$$$ into making a user-friendly client for an established/reliable protocol.
In this sense, and despite all my criticisms of email/XMPP ecosystems, i'm a big fan of delta.chat and conversations.im. They took a well-established federation, and applied lots of UX/security on top, so that people don't have to choose between freedom and security, and can enjoy modern features in backwards-compatible, federated way.
> Signal isn't perfect but it seems to offer better privacy
Compared to SMS yes. Signal evolved from smssecure/textsecure which was an encrypted SMS app/protocol (which continues to this day as silence.im though barely maintained by a single exhausted volunteer).
But Signal is a central actor that has power over all users at the same time (compared to a federated network like email/matrix/XMPP) so it's less healthy. And in particular, Signal uses servers from big internet giants which thanks to signal using Google's push notifications server on Android (the reason why the libresignal/f-droid vs signal "controversy" started) can give them a really good overview of who's talking to who.
I trust that Signal employs some really clever cryptographers and very competent UX designers. I just don't trust anyone (including myself) to hold the privacy of the entire planet, even less so when their plan to protect metadata relies on shady tech (intel SGX) and shady actors (amazon/google) not proper systems architecture, and they have openly/strongly opposed decentralization and standardization/interoperability (see "The ecosystem is moving" and/or the libresignal drama).