And this is literaly what they're doing with RCS - it's a carrier standardized protocol to upgrade the existing SMS functionality. I wish you'd read up on it before you fell into this complete rant.

RCS also beautifully demostrates the problem with these open protocols - carriers simply refused to support it and federate between themselves, so you couldn't even send a message to a non-carrier branded phone, even if your exact carrier supported it. They (with push from governments) even demanded it's unencrypted.

This is Google basically stopping to wait for carriers to stop screwing their users and allowing some users to get this messaging protocol without waiting for their carrier to stop being incompetent. Unfortunately they're also going about it in the typical Google way with insane rollout rules.