> And you can't even implement it yourself because it requires special permissions on Android

That depends on your carrier, which is even worse. There are several ways to activate RCS for a phone number, as this standard is meant for carriers rather than app developers, and the carrier gets to choose which one they want.

I think the reference implementation died around the time carriers shut down their RCS servers because nobody was using them. https://github.com/Hirohumi/rust-rcs-client seems to be the most reason open RCS client at the moment (with an Android demo app).

The real need and opportunity for an RCS messenger is on the LineageOS/custom ROM scene, where these permissions are available (you can sign the ROM yourself, after all).

As for the Google stuff, RCS being routed through Google is an anomaly that will hopefully be fixed as carriers add support to it so native Android <-> iOS messaging isn't completely terrible. Progress has been slow outside of countries that still use SMS (like the USA) but eventually we'll be back to normal carrier-based carrier message exchange once things calm down a bit.

On the Android side of things, I don't expect things to change soon, as most of the restricted fields were at one point available to developers and were mostly used to stalk users across installs without their knowledge for tracking and "telemetry" purposes. A country where people actually use SMS/RCS will have to crack down on Google's lack of an RCS API.