Outside of hints from story elements within the game, most of what you'll either outright learn or get teased from involves the Fanfests. There are 3 fanfests overall and we'll learn new things for the next xpac at each one/get hints towards certain things as well.

We'll almost certainly learn of one new job at the first fanfest as well as the area we will be going to.

Basically we'll start actually getting info for the next xpac during/after 4.4.