Disney has recently released a new survey that asks what characters you want to see in the future.
If you remember the last survey, many characters that made it into DI2 were on the list; this includes Stitch, Merida, Black Widow, Iron Man and more. I believe that there is a large chance some of these characters will be seen in DI3: note that just because they are on the list means doesn't mean they'll make it into the next iteration (Wall-E and Mario were on the 2013 list, for example).
In categories, here are the characters listed.
STAR WARS (!)
Princess Leia
Chewbacca
R2D2
Darth Vader
Obi-Wan (young)
MARVEL
Ultron
Loki (?)
Black-Suit Spiderman (??)
DISNEY
Mulan
Baloo
Cruella
Olaf
Minnie Mouse
Aurora
Tron
Cinderella
OTHER
Violetta (a latin american disney channel star!)
Star Wars is no surprise at all, but seeing Mulan, Baloo and CRUELLA of all people on the upcoming Disney list make me very hopeful indeed.
I do have to wonder what the point of putting Loki and Black-Suit Spiderman on the list is however.