I was visiting Daisy Ridley's IMDB page and noticed that she had a credit for Disney Infinity 3.0. I checked it out to see the list of voice actors. Not every released character has a credit, but there are many credits for characters that do not have a figure. Granted, some of the voice acting may be done for the playsets and doesn't necessarily mean they have a characters coming, but some may be unknown. I'll admit I haven't played through any of the playsets, so I don't know if some of the characters have an explanation that is already known, but here is the list of unreleased characters that have voice actors attached:
Cad Bane
Mace Windu
C-3PO
Aayla Secura
Padme Amidala
General Grievous
If any of these characters don't have speaking parts in the playsets (again, I haven't played them, so somebody can fill me in), it is a likely indication they have figures coming.