yeah, we actually don't know that much yet. but there are a lot of Disney worlds that we haven't visited yet.
i watched a review at IGN, and it appears that Square's got to ask permission to Disney to use certain worlds. so that could make it difficult to make new worlds again.
and it's difficult to say if there are going to be a lot of persons who buy KH3. if it appears for the PS3, it could be that a lot of fans drop the series 'cuz of the price. admit it, it's not going to be cheap.
it wouldn't suprise me if they were going to make a movie about it. like they did with advent children... but then again, only time will tell ^_^
and i'll try to follow the rumors