Scarecrow season 1 promotional artwork

If the show is indeed picked up for a fourth season, Danny Cannon has mentioned that he intends to reintroduce Jonathan Crane in order to do a Scarecrow story arc. Clayface's character will also be explored more in the next season. Although not officially confirmed as of yet, it has been suggested that Barbara Kean will act as a precursor Harley Quinn.

Fingers crossed that Fox do greenlight a fourth season.