[mr90210]

A few months ago I had thought about this topic, what I had in mind was some sort of protocol for Messaging which Messaging Apps could agree to adhere, thus making interoperability possible.

As the article says, that’s not a trivial problem, nor do these apps have the incentive to adhere to such solution unless they are a new player.

[bilal4hmed]

For the protocol Matrix would be a good fit but all the other points you mention are valid. Its not trivial and there is no incentive.