So as some may know, Ferb has been seen as a playable character in a few trailers... however, he is missing from the Hall of Heroes. But he certainly exists. And there is even a costume for him (You can go see it in game in one of the Creativi-Toys tutorials.) That costume is not in the Disney Infinity Vault, so the only other place it can be unlockable is a character chest or vault. (Character costumes for a figure are normally located in their first character chest.) Ferb could very well be a Wave 3 character, if a Wave 3 exists. In addition to Ferb's costume not being in the Disney Infinity Vault, I noticed two other important characters' costumes are missing as well. They are Aladdin and Beast. Jasmine, Genie, Belle, Gaston, and Jafar all have costumes in the game, but neither Beast not Aladdin, bth main characters of their movies, do not. This doesn't mean they are playable, but they could be possible future figures.
Edit: I searched the collection for an Aladdin or Beast Costume. Neither are currently in the game. However, costumes I did find with no matching playset or vault unlock are: Olaf (Frozen), Cruella De Ville (101 Dalmatians), Evil Queen (Snow White), Maleficent (Sleeping Beauty/Maleficent), Ferb (Which we already knew was in the game anyway), Candace (Phineas and Ferb), and Dr. Doofenshmirtz (Phineas and Ferb). (Edit 2: Also Sally from Nightmare Before Christmas.)
Finn McMissile's Paint Job (The Cars version of Costume) also exists, but that may be unlocked from the Cars playset, a playset I do not currently have.
Again, this doesn't mean these characters will exist as figures. They may be unlocked through other means.
Notably, Candace and Dr. Doofensmhirtz are both main characters of Phineas and Ferb, like Phineas, Ferb, and Perry are.