"But now Google is taking over: later this month, Android users in the UK and France will be able to opt in to RCS Chat services provided directly by Google instead of waiting for their carrier to support it."[1]
Sounds like we might get some movement on this soon, as Google is offering their own servers as a fall-back in the case that the network provider hasn't provided their own.
1: https://www.theverge.com/2019/6/17/18681573/google-rcs-chat-...
There are about 800+ mobile phone operators around the world and based on reports about 50 or so have signed up. Not a great percentage after 10+ years.
And I think the lack of encryption is going to kill adoption in many parts of the world.