Earlier quoted context omitted.
Re. being able to switch carriers and still communicate, what happens when you travel and (temporarily) get a local SIM? Are you suddenly messaging all your existing contacts from an unrecognized foreign number "Hi, it's John, this is my temporary Thai number..." and then relying on that message not getting binned by some spam algorithm? What prevents carriers from charging extra for RCS messages originating abroad?
In France we get to keep our phone number when we switch operators. Travel is an issue yes, but I think it's worth it to have a truly decentralized system.
But I'm concerned that the intransigence of carriers, especially those that operate in non-competitive environments, will get in the way of rolling it out properly and effectively.