I really don't know who should take over the series next. After playing through The Elder Scrolls V: Skyrim, I personally would like to see what Bethesda Game Studios would do with Castlevania.
Regarding From Software (Demon Souls/Dark Souls), I'm not sure. From what I've seen, their games are excessive hard and unforgiving. Plus, I heard that if you die once, you have to start all over from the beginning. That being said, they could really nail the atmosphere.