I wouldn't say Android is switching, I'd say Google is switching. There's no support in Android itself. Third-party SMS apps cannot hook into RCS. There's limited carrier support. Google is running the RCS relay, and it's only at the app level, not the OS level. This might seem like an academic distinction to some people, but certainly not to the billion or so users in China, anyone who likes third-party apps, or anyone who prefers deGoogled Android OSes.
Most carriers still don't support RCS themselves, Apple would need to build their own relay like Google did.
RCS itself is not necessarily E2E encrypted, though Google has hacked that on top if you use their app. This is not an improvement over other closed systems like iMessage. It's just another closed system.
And because it's Google, the left hand has no idea what the right hand is doing. Doesn't work on Google Fi or Google Voice, last I checked.
You couldn't pay me to adopt another Google messaging platform after they've jerked me around endlessly with g-chat/Hangouts/Duo/Voice. I'll use RCS when it's truly open and standard. As long as Google is the gatekeeper, I'm out.
The whole system is a mess, largely thanks to Google's mismanagement.