I do not know about the next to next expansion, but the one after BfA could very well present no new areas. I mean, Blizz has an entire mass of levelling areas that have been untouched since 2011. They could easily update the entire Kalimdor and EK, make new threats and refresh the experience on what represents the most massive land in the whole game. At the end of the day, it is a new story and new quests that make the story and not new geographical spots, right?