I don't think the Turtles will be a fail and I'm actually hoping that it's the best selling DLC character, given their past track record with DLC characters.
Actually, a huge part of me hopes that NRS is testing the waters with this DLC, and then Viacom (or whomever now owns the TMNT rights) gives NRS the greenlight later to do a full fledged TMNT fighter in the vein of Tournament Fighters.
Yeah, it's a pie-in-the-sky dream / wish / hope, but I really hope that sometime later we can get a full Ninja Turtle fighter from NRS, much like how MKvsDC came out first and then later we got both an MK AND an Injustice series out of NRS.