Oh man, so many things that at that point it wouldn't be retail anymore. I don't keep up with retail news so some things I'd like might already have been done.

1 - LFR gear being on par with heroic dungeons gear so it doesn't go into the gearing loop for raiders that aren't skilled enough to go straight into m+ after a break.
2 - Transmog gear not working inside raids so you'd still have to put in effort on current content to look cool.
3 - M+ having a daily limit on it dropping gear so, again, middle of the pack raiders wouldn't feel pressured to run m+ non-stop in order to feel like they've done all they can to gear up inside their skill bracket (high level raiders don't have this issue because they quickly progress to max m+ gearing brackets and have to run dungeons a lot less to be BiS pre-raid drops.
4 - Profession catch-ups if you made mistakes at the beginning. This is actually why I went back to classic, at some point my things were being sold at a loss and I had no way to change that without losing all my current progress by dropping it and picking it up again.
5 - Less bouncy animations for races across the board. At least for humans.
6 - Less things popping on your screen and yelling for attention at all times. I haven't been 15 for a very long time and I don't play mobile games for the same reason.

I think in the end even if I do WANT to play retail, I think my hopes lie in classic+ or classic up until MoP