That doesn't mean we'll only go to seven worlds, but I definitely agree this could be a quality over quantity thing. I'd rather visit less worlds and have a more cohesive story and large areas rather than many worlds and flat worlds with a disconnected story.
Somehow I want to say that Traverse Town doesn't count, but it might end up that way.
Traverse Town
La Cité des Cloches
Prankster's Paradise
Country of the Musketeers
Symphony of Sorcery
The Grid
That's six confirmed worlds plus we know we'll be in the World that Never Was, we'll see scenes from Destiny Islands (almost certain it's our tutorial world for basic gameplay mechanics), Radiant Garden, Mysterious Tower, and we saw the Chamber of Waking which is in the Land of Departure...
If you're wanting for another Disney world, I dont know what to say. Hope for another world that is unannounced? Don't and be content with what we've been shown?
IF you count DI and TWTNW, you have about eight potential playable worlds.