Apart from better media, typing indicators, etc., RCS allows richer metadata (like content types) and various side channels (AFAIK) that allow extensions like E2E to be added. SMS is just 160 characters.
I believe Google will share their E2E spec with others. They published an overview a while ago [1], but presumably they'd offer more to someone wanting to actually implement it.
Better media is a valid point, but I feel like mentioning typing indicators right after totally takes away from it. It felt so out of place in the article as well. Sorry, but who gives a fuck? All you need to do is wait a couple more seconds and you will know whether the recipient got your message, because in 99/100 cases, guess what follows the typing indicator? A message. I honestly do not get the benefit. If anything, it stresses me out.
Sorry to pick and choose from your comment. Like I said, the other points are definitely valid. It's just this feature I don't understand bringing up.
The actual "open" parts of RCS don't seem any better.