From IGN: "Shredder's Revenge publisher Dotemu has clarified that, while the TMNT game won't launch with alternate costumes at launch, and there aren't DLC plans currently, the team has not ruled out adding new content in future.
On Twitter (below), Dotemu CEO Cyrille Imbert said that any future DLC would "depend on many factors like the game's reception and the ideas/feedback that the awesome community will send us."
Turn the effort into a new game. Fing dlc is the worst. Makes games feel and sone actually are incomplete. To this day i feel dlc is the worst thing in gaming counting micro transactions in there to.