That last sentiment would be very nice indeed, but I fear this is what we'll get instead:
Why? Unlike Matrix it's actually an Internet Standard.
But if I would have to bet on a standard which could become it right now, then it would be Matrix.
It convinces when it comes to adoption, concept, features and growth.
Should this be fixed (e.g. through regulation), XMPP is absolutely a sound choice - given, as you say, its 20 years of experience, evolution and deployment track record.
In theory, you could achieve with it what Matrix achieves, but it would probably be more feasible to start from scratch - like Matrix did
That said, I see how it currently has advantages when it comes to resource consumption as well as internal deployment to centralized services.
Note that sometimes new standards are promoted specifically to destroy an existing open standard. The trick is to push hard for the new standard until it gets sort of popular and then back off. Adjust as required to keep things balanced.