The RCS bubble will at best be a color other than blue. The whole "blue bubble" class stratification is a competitive advantage for Apple, even if it's not truly earned. RCS provides a lot of the features that have made iMessage a preferable experience. And over time the collective consciousness may drift towards inclusiveness or indifference towards whatever bubble color RCS turns out to be, but I feel confident that unless it's mandated by some government body, Apple will keep blue bubbles to exclusively indicated iMessage.