This thread is interesting. I had not heard of RCS.
RCS looks like a positive development from the point of view of standardisation – if people use RCS instead of proprietary messengers that can’t have Free Software clients then it becomes less problematic that neither Purism nor the community can develop such clients. This is not as good as a decentralised platform detached from the carrier altogether, but if you’re using carrier services like SMS already, then RCS is probably not a downgrade from that position unless it displaces use of non-carrier-bound services, such as email.
But it looks like it has the potential to be a negative development from the point of view of privacy. The GSMA’s website features a slideshow which highlights “True metrics” and “Read receipts for brands” as features. There are also ‘presence’ features (online/offline status). A Librem 5 RCS implementation would need to offer the user full control over those! I wonder if the design of RCS enables the classic tracking images, as used in HTML-format marketing emails. That could be annoying.
It could be annoying as a user if businesses start sending you massive graphics plastered with their brand identity when a simple SMS would have communicated the same information with less superfluous marketing cruft.