I don’t want to go too far off-topic but this is something I do not understand about RCS. This is a complete Google-thing since most carriers do not provide an own server but rely on the Google one as it is cheaper for them. So even iPhone user are using a Google service here, and if SailfishOS would support RCS you would have a constant connection to Google if your carrier is using Google Jibe. Is this really better than an optional client from Meta with e2e encryption?
Besides, even on Android the Google server is refusing connection for rooted and unlocked devices, do you really think they would allow a SailfishOS implementation?