Androids RCS adoption is good with major caveats:
- it's good only in certain locations, without global ubiquity
- it still very much depends on what phone you have
- it's only recently become good enough to be usable
- it's still tricky to deal with the SMS fallback problem, and you'll still see Android phones struggle with SMS fallback
So in the case of iMessage, for them to adopt RCS they'd need three tiers of messaging:
- iMessage (because it's not just for cellular devices)
- RCS (for those devices that handle it)
- SMS for everyone else
People act like RCS is a solved problem. It's not and while I'd love to see it integrated into iOS, it's not as trivial to do it as just saying: okay add it in.