He did say back in 2014 that there would be more worlds than in KH2. However, take note that the strongest system they have released a game on was between the PS2 and the 3DS. That was probably during the time that they have decided to go with quality over quantity. So far, we only have 5 confirmed Disney worlds (Hercules, Tangled, Big Hero 6, Toy Story, and Monster's Inc). I'm guessing we are only going to have about 8-10 Disney Worlds and about 3-4 original worlds, 14 total worlds at the most and 11 at the least. At this point, Frozen is basically 97% confirmed to be a world (there's still a chance of it not making it in, but let's be real, Square would be idiots not to implement Frozen into the game). The Jungle Book and Treasure Planet may have a chance, but a very low one. I would think Princess and the Frog, Wreck-It Ralph, Wall-E, or even Star Wars have a better shot making it into KH3.
Other than that, modeling takes time, especially on a more developed console like the PS4 and Xbox One. Also, they listened to the fan requests on not making the worlds empty. Only time will tell how good these decisions were made.