Regardless of what you think of Zelda, I believe an actionpacked Zelda-esque Castlevania would be quite awesome. The game would be built like, say, Twilight Princess with a huge, gothic overworld with forests, dungeons, graveyards, mansions, villages and castles. It would also be rather cool if you could see Dracula's castle in the horizon, but being unable to reach it until the very end of the game or summin'.
The gameplay would basically be castleroid-ish in 3D. Yeah, I know this sounds an awful lot like Simon's Quest in 3D... You would gain abilities as you progress through the story (much like Zelda, Metroid etc), so you wouldn't be able to cover the whole map immediately.
It could have both action, platforming and lighter RPG-elements to satisfy most of the Castlevania community. I think it could work, but I realise it's a HUUUGE undertaking to develop a game like this...