I think there's a huge problem facing the MMORPG genre, and that is that it exploded into popularity so hard with WoW's over-success that it attracted so many types of players who's fun is entirely compartmentalized and couldn't care less about the overarching game world. They either raid, do some dungeons, or PvP, or collect things. Roleplaying and socialization aspects have been taking a backseat for years now, it's nothing new and I won't bore you with more talk on this.
I had a thought, though, and it's pretty sad because I'm probably completely on the mark here. I think if someone came out with a new type of sub-MMO genre that completely eschewed the world out of it, it would be really successful and suck up a lot of these types.
Imagine logging into a game where all that's offered is a chat lobby with chat channels, a friends list, and the ability to queue up for different types of content. Raids are there, dungeons are there, PvP arenas are there, Battlegrounds are there, they have all their usual bells and whistles with the multiple difficulties for some and achievement hunting etc. You could literally relegate old world mog farming to a gacha type of game and people wouldn't notice a difference. When you queue up for a raid with other people, of course you zone into the actual 3D instance of the raid and do that as you normally would. Same with dungeons, arenas, battlegrounds, etc.
Leveling and professions could be entirely removed and the beginning of the game starts you out with some basic gear and a training mode scenario to learn the class. The game is just about farming loot so you can farm harder difficulties and get achievements, pets, mounts, and mogs etc.
People wouldn't hardly notice a difference and would play this kind of game possibly even more than they would WoW.