I have no idea how outsourcing really works, but I was thinking that maybe From Software is a little too big to be doing someone else's game? Again, I have no idea how things like this work, but normally you'd see the likes of Konami and Capcom outsourcing to rather small and sometimes completely unknown studios.
Well, SquareEnix did "outsource" Dragon Quest to Level5, but that was before Level5 became as big as they are today (with the Layton series and whatnot).
As much as I'd like From Soft to make a Castlevania game, I think they'd be better off - financially - making another Souls game. Not to badmouth Castlevania, but my guess is that Dark Souls 2 will outsell Lords of Shadow 2 quite a bit... Even though LoS2 arguably looks like the more "mainstream" game of the two. I guess time will tell, but those are my two cents...
HOWEVER, with the right kind of marketing, i think From Soft would be a great way to really make Castlevania hip, or something. But that would have to happen right NOW when From Soft is still hot and happening... not in 3 or 4 years.