It’s a shame Phil Schiller has gotten sidelined. He always seemed like a good guy and a big part of the “soul” of Apple as it made its resurgence under Jobs after the NeXT merger.
How do I know it was probably illegal? Because Apple finally caved and implemented RCS once it started leaking through backchannels that a legal case was being built against them.
None of the services you listed do it, but that's because they don't want to, not because it can't be done. It's a business decision problem, not a technical problem.
https://9to5google.com/2025/03/14/rcs-end-to-end-encryption-...
https://www.theverge.com/2021/4/27/22406303/imessage-android...