Recently, Fred Seibert of Frederator Studios was on the Nickelodeon Animation Podcast discussing one of his upcoming projects. On the podcast, he mentioned that he's working on an animated project tied to one of the biggest game franchises in the last 30 years. While the speculation naturally lead Nintendo fans to get excited, it seems like the project might be tied to a long-running third party franchise.
Back in 2015, producer Adi Shankar said he was working on a "super violent Castlevania mini-series". In that same declaration, Shankar said that he was working with Fred Seibert on the project. To go further still, it appears that Frederator has owned the rights to a Castlevania cartoon for over 10 years now.
As you can see, there are certainly a lot of points that line up. It's not a done-deal, but it's looking pretty likely that the project is tied to Castlevania. Obviously if the series is going the super-violent route, it's not going to appear on Nickelodeon. As we stated in our original interview, just because Seibert was discussing this project on the Nickelodeon podcast doesn't mean it would air on Nickelodeon.