What you are describing is basically the gap that Snikket aims to fill - although for personal communication, it's not particularly aimed at organizations (I think the requirements for that are different, and there are many existing options already).

I know at least one project aiming to fill the same gap for organizations though (again, using XMPP), but pre-release currently: https://prose.org/

I'm a firm believer in essentially what you said: The protocol doesn't matter, it's all about the products and what they can do and how easy they are to deploy and use.