Koji Igarashi, producer for many of Konami's Castlevania games, recently admitted to having started work on ideas for 3DS.
An in interview with Destructoid, Igarashi mentioned that he has plans to work on the new Nintendo hardware, with ideas still in their early stages. However he does possess a development kit and is testing and getting to grips with working for 3D.
The face behind Castlevania also confirmed that he is crafting many titles for Konami, some unrelated to the longrunning vampire series, with a Igarashi "unsure how long we'll have to wait" for a new 2D entry.
Would you want a new Castlevania game for 3DS? With support for both Wii and DS being fairly strong recently, it's likely a new entry or remake will come about at some point.