RCS will not succeed if all the SMS/MMS app developers do not get on board and implement it in their respective apps. We have such a wide variety of apps we can use that it actually creates a problem when RCS drops. If a dev decides not to incorporate RCS, the feature is dead on arrival.
Textra, Yaata, Signal, Mood, Chomp, EvolveSMS, Handcent are the ones I can think of just off the top of my head and I'm sure there are more. Textra has said they will incorporate RCS as soon as the API is available, but what about the others? What about all the carriers? Google has really dropped the ball when it comes to messaging and I think they were closer 3 years ago with Hangouts than they are now. However, the fact that the US and its carriers are still using SMS is the reason we are in this situation in the first place.
I also agree about Apple incorporating RCS. My entire family including extended family are on iPhone except for me. If there is a video to be sent out, I'm left out of the message because they don't want the video quality compressed because I don't have iMessage. They also refuse to download a chat app because of the beauty and simplicity of iMessage (can't say I blame them).