I hope there's a new [non-mobile] Castlevania game in the works, but I have a feeling that the Smash Bros. thing is just something that Konami can put little or no effort into while making some money (presumably). If Konami doesn't feel like having a new Castlevania game developed, though, then I'd settle for re-releases of the originals. Also, Castlevania: The Adventure ReBirth really needs to be re-released, as it's a great game that I really hope isn't limited solely to the Wii eShop (especially since you can't add eShop points anymore).
That said, what would make the most sense to me is a remake of Castlevania III: Dracula's Curse that more closely follows the events of the Netflix series. I'd actually prefer for them to take another shot at updating SotN and not half-assing the new content this time.