RCS is a replacement for SMS/MMS all the modern smartphones are incorporating that has end to end encryption of message contents (note: see privacy issues with cellular providers overall). The issue is they're not as open as the predecessor.
if support for RCS begins with a Play Services requirement, then people who don't install RCS will only have SMS/MMS, it's that simple. We won't be bundling Google apps or services into GrapheneOS. They need to choose it.
