Pure speculation, but it would be kind of cool.
Queen Jennah and the 5 members of Destiny's Edge are murdered, a new dragon rises and sinks Lion's Arch for good, and everyone escapes through the giant doors guarded by the Tengu which are guarding the portals in the trailer. We get the first look at a new continent, new race, and brand new story. It's been a year and a half, I wouldn't be surprised if they revealed an expansion.
Or Scarlett attacks LA, we kill her, and nothing really happens at all. Probably that.