Also you can’t really use Apple TV properly without an Apple device. Same with iCloud. Actually really any service they make only works properly with their full stack.
AFAIK Apple has said they are only going to use official RCS spec with no extensions and will work on adding encryption to the spec. Google has announced that they will work with Apple and the GSMA to implement official RCS encryption.
Also you can’t really use Apple TV properly without an Apple device. Same with iCloud. Actually really any service they make only works properly with their full stack.