Unicode being widely adopted (which is what is happening) is the solution to the problem you seem to have of Unicode having to add more codepoints for compatibi

Unicode being widely adopted (which is what is happening) is the solution to the problem you seem to have of Unicode having to add more codepoints for compatibility with other encodings. Even if the pre-Unicode encodings never go away, they've already taken their respective bites out of the codepoint space, and they won't take up any more of the Consortium's time. The only way this becomes a live issue again is if someone develops a whole new encoding which is incompatible with the latest version of Unicode. And it gets enough traction to get on anyone else's radar. I simply can't see that as very likely.