I've always been a fan of the warcraft lore since I started to play wow, including the warcraft series. The first threats you faced were the small ones for each race, for example, kobolds and defias for humans, frostmane trolls for dwarves, satyrs and demons for night elves etc.
What could be real nice, is that if Blizzard released a "filler" or a break expansion where you don't meet a big new boss threat and where Azeroth is kinda at peace for once? Instead, why don't we bring up the old battles and problems that occured in Eastern Kingdoms and Kalimdor?
Instead of one huge threat, I suggest having tens of small threats around the world and flesh out the lore that we never got to finish? We could continue the Kul tiras lore that disappeared, or Bloodsail Buccaneers starting to attack the docks, kobolds rising up, satyrs planning something shady, new band of Defias Brotherhood gangs or a new similar group cooking up problems. Here's a map of factions up to wotlk.
This would mean that we would go back to our Warcraft problems that we had back when we first started out, no new huge theme that we've had for the past expansions (the demon theme is getting really spammed). However this all would feel a bit weird after us defeating strong ass demons, gigantic dragons, old gods and the burning legion.
I feel like this could be something nice, but that's probably because I love playing in the vanilla continents where every zone had it's own storyline. It's a shame Blizzard left them out. What are your thoughts?