Google will begin rolling out RCS support to all Android devices today. The rollout will happen in stages. Additionally, RCS will only be available through Google's Messages app. However, the rollout will eventually come to all Android devices, replacing the outdated SMS system currently employed.
https://www.notebookcheck.net/Google-begins-rollout-of-RCS-rich-communication-services-text-messaging-for-all-Android-users.442799.0.html
Funny enough, I noticed that my Grandma's phone had RCS already a good week or so ago. She had a typing bubble in Google Messages on my side, which was kind of unexpected. I had RCS activated manually for a while, but it was the first time I actually was able to use it/see it.
So, does this system require a data connection or can it work completely without one just as SMS does? I've had so many people come to me saying their messages have been delayed or not sent at all and the problem has been that some messaging apps have, for some dumb reason, automatically switched over to using some service that requires a data connection instead of just sending a classic text message that always works...