iMessage works.

So does 4G. Imagine if apple refused to support 5G? Yes the end consumer might not notice but apple refusing RCS is them refusing to update an old standard to it’s next version. I guess they dragged their feet with USC C and kept with a old USB 2.0 lighting cable for so long…

They could adopt RCS. But still keep iMessage users using their iMessage service backend and have the green/blue bubble thing still.