No offense, but that seems a little cliche to me. It seems like there's a lot of fiction out there about the Nazis messing with the occult and reviving ancient evils and such. That might've been more expected for PoR than the plot we ended up getting.
Cliche, for the fact that it's an idea that's been done, maybe, but you can say, within the CV series, the whole "Dracula being resurrected by a cult" or "yet another Belmont faces against Dracula" is just as cliche. Hell, it would be as cliche as every take on Dracula(despite the little things that make them different/unique), every take on possession, ghosts, the whole "god is really an alien and mankind was an experiment", and the "Wait! I was dead all along!" type story. There's nothing wrong with a simple, shared base idea, it's how it's executed that makes it worthwhile. You could have five titles that, simply put, are about heroes rescuing princesses, but the meat of the game and what transpires are all very different from each other. Take an example the movie Inception. Some might think it was orignal, the idea to enter the dreams of other people to influence them and such. It WAS done prior to that, though, in the movie Dreamscape. The only thing is, Inception did it's own thing and did it well. Base concept's pretty damn close, nonetheless(using dream interaction to influence the sleeping person, or help them psychologically to deal with issues, or even KILL them). It's the spin you put on it that makes it unique.
I think people wanted the whole "Nazi occultisim" because, seemingly, there WAS a group that DID dabble in the such. Were the conjuring demons? No, but it WAs still something that went on, and the mysteries of such intrigues people and imaginations run wild. It's similar to the whole "secret history" theme of various stories(Castlevania included). That there's this shadow of events that happens under our noses, kept from the history books, covered up by the governments of the world to keep us in ignorance(in CV's case, for the greater good). Whether it's been done before, so what. It's been done, will be done again, and so on and so on. CV could've put it's own unique spin on it, and that would've been one I would've love to see.