I like the idea of spontaneous world events like Rift. With Wrathion hinting at another Legion invasion with the meteor thing, I could see that happening in concurrence with SoO. Maybe have SoO out for a couple months and while we are knee deep in Garrosh blood, the invasion starts. Random Legion events all over Azeroth scaled to the zone they happen in. They could make it so the mobs health/drops scale to the amount of people who tag it and could make leveling a little more interesting as well. This could slowly ramp up and culminate in a single boss raid to bridge the gap to the next expansion.