I think the hard part about doing a vertical platforming segment is that most 3D platformers, while platformers, are still trying to maintain this sense of realism in the game. And, from what I've seen in several games, realistic vertical platforming segments are really hard to do. Just look at CV64, for example. Granted, the villa was the only really "realistic" portion of that game, save for a couple other areas.
I would like to see a new 3D-vania apply these segments, though. If we got another "spooky" CV (a la CV1 or CV3) rather than a "horror" CV, than there would be no need to focus on realistic looking environments.
I don't think realistic should be an issue regarding a demon castle that can take many forms. What I liked about Olrox's Quarters in SotN was that to reach him, it was almost tailored for a vampire(long vertical shaft in the ceiling). Similar to the "heart" in the center. It's layout should act as an obstical in itself. Besides, I'm kinda sick of realistically designed locations. Dracula's castle isn't meant to entertain human guests. It should fit him and his monstrosities in a similar fashion the subterranean caverns in The Descent best fit those "Crawlers", not the human explorers.
That's kinda why I never questioned the strange platforming in CV games. I always figured, it's a vampire's castle filled with undead things that can leap and crawl all over the place. Any mere human would find it nearly impossible to traverse, while a Belmont would take the obsticals head on(because they're badass like that).
At least, IMO, that's a valid excuse to go with a less realistic layout.
Technically, I think it would be harder to program, but I DO think it's something that should be addressed, if not solely for CV, for the future of gaming altogether. Most hurdles regarding game design have been encountered, and though hard work, mistakes and pinpointing the problems, they've been surpassed. One example would be fixed cameras. It might not be perfected, but it's sure a helluva lot better than years ago, when it was more prone to get wonked out. It takes great minds to tackle this issues and when they do, that's a step gained towards a better gaming future.
The thing is though, the cheesy monster movie feel is the strongest in the original, and it gradually waned after that. You may have to ask yourself if the series is still about that at this point. I actually really like the idea myself. A game that just embraces the campiness and rolls with it. I wonder how people would react if that really happend.
I'd be SOOOO for it. A total Hammer-influenced Castlevania game. I love that style of horror. I HAVE been aching(for a while now) for an 19th century set CV(not like the ones we got) that reflects that visual style you'd see in a Hammer movie. Something like the Lee Dracula movies, or even like The Gorgon.



Or even the Brides of Dracula:



.... DAMN!!!
Something like that in style. Look at the last picture and the use of color regarding the back room and purple-ish light off to the side that's reflecting on the floor. Something like THAT! I'd stake a few vampires for a CV game like THAT!!!