What is "true" Castlevania?
Before SotN, people said it was timelimited platforming. After the worst of the 3-D games, it was SotN. When SotN clones kept pouring in, people wanted to go back to the basics.
I don't think there is a definite style of Castlevania. As long as there's good music, gothic imagery and action, it's Castlevania to me (even if it's a shitty Castlevania). Even with the change from Beefcake Barbarians to Attack of the Bishies or repetitive hack'n slash I feel the atmoshpere has been kept. I trust Kojima would catch that same drift even if he were to implement his convoluted and sometimes silly plots into CV.
What I'm saying is we shouldn't be so rigid about this. 2-D can't go on forever and with 3-D attempts having been mediocre at best (by any game standards), I don't see 2-D being an essential ingredient for a good CV.
Edit: Danial, you bastard. You beat me to the punch