Unfortunately, RCS on Android requires google apps, so this isn't really a solution to anyone who doesn't want to be tracked by Google everywhere they go. I'm still a little confused as to what problem RCS is supposed to solve. It is just as centralized as any other chat app, and is a bit more invasive (often requiring device attestation). Is it really worth all this hassle just to not have to install, let's say, Sig…
Anyway iMessage (and iOS for that matter) is irrelevant where I live so I don't expect this to change anything. I'm not going to be on RCS. The main apps here are WhatsApp and Telegram (the latter more for groups)