To be honest, a new zone is highly unlikely unless it has been in works for a while. Playable zone is much harder to create than less say creating a hero. Even with a hero, new heros are more resource-intensive to make than re-paint ones. ( And see how many re-paint vs. new ones we got).
Also, heroes can be sold. Not sure selling the zones or paying toll to play in a premium zone is feasible. Otherwise, there is no financial incentives to create new zone at all. Just my 2 cents.