You act as if they haven't run the existing lore through a paper shredder already. At least a world changing event would be awesome between the retcons and non-stop pop culture jokes.
Of course that's easier for me to say because I've never cared for Warcraft lore.
If I could have one feature in an expansion it would be:
Difficulty.
Somewhere, anywhere outside of hard mode raids. My main complaints about World of Warcraft and why even after three or four years of playing it that I don't find it very memorable is that:
1.) I've never once felt challenged by the game at all in PvE, even in hard mode raids I always felt like it was one of the twenty three (I perpetually duo'd with my best friend) other people. I'm not the best player in the world, and I'm getting old now! Almost 24! But I do play a damn fine Priest and I am good at blaming people.
2.) I dont like the story or characters, this is a personal thing that I don't put any blame on the game for.
I would sign right back on if they'd announce some systems to really make questing and small dungeons a progressive, challenging experience. Even if it was just silly shit like limiters from FFTA or Fable or what the fuck ever. I like hard games and I like team oriented games.
WoW is so easy to pick up, I just wish they could combine that ease in conjunction with systems or options that really made it feel meaningful to quest with a friend or do small dungeons when it wasn't raid time.
It just makes me sad that I have all these memories of really difficult situations from leveling in FFXI back around launch or playing two player Monster Hunter and beating insane encounters through pure skill, but I dont really have any memories like that of WoW. Just mow through quests to get to cap so it feels right to be in a team again.
Challenging RPGs where you just barely scrape by encounters by the skin of your teeth is my favorite thing in all of gaming.