Personally I think that if d3 goes with expansion they should bring 1 or 2 new classes(everyone would like necro to be back) and NEW sets(not remake of the old ones) so that we take advantage of the classes in different ways. It's not nice to have specific classes in the leaderboards. Everyone should be able to be as long as he is really well geared. Also the game seems to have issues like lag caused by things like area damage..annoying right? Just remove it and change the way some spells deal damage..and fixed.
The point is competition since all of us have heard about Lost Ark and Lineage Eternal being on the way. And they seem really well made. So what could bliz do to be competitive? An expansion on a game that is losing fans due to not having new ideas and you get bored to play just the same thing every season with minor changes or a new game that could bring the Diablo franchise back to life?