One of the few things I enjoyed in Rift were the rifts. I think something similar in WoW would help the world feel more alive and give another reason for people to be out in the world. I know that initially it would take a lot of work to add, but once in it would be easy to expand into each new area. In Outlands they could have random Burning Legion attacks, in Northrend you can have Scourge attacks, Sha or Mantid in Pandaria, Horde/Alliance invansions in the Kalimdor/Eastern Kingdoms ect. What do you all think?
Edit: As mentioned below, GW2 had great dynamic world events that are more like what I was thinking for WoW.