It's going to be a long process. Mobile carriers, like mine (O2 UK) don't really stand to gain anything from RCS. Until companies begin to offer additional functionality for RCS users, like branding, rich media and bespoke action buttons[0] and normal people start moaning or switching to a network that does support it, I really can't see them budging on their stance.

[0] https://www.openmarket.com/blog/rcs-to-eclipse-apps/

I was not aware of RCS until today. Looking at it I can see governments also being very keen to see it take off; since many of them are worried about end-to-end encryption hindering their ability to snoop on private conversations.