"2.5D" is pretty neat, especially when the games don't strictly move from left to right. I mean, mechanically they still do—the play control is still the same, essentially—but the foreground can bend and curve and do all sorts of cool stuff, that makes it very fascinating.
However, a console sprite game would be awesome for Castlevania. Higher resolution has rendered pixel art almost impossible (unless the artists are insane and really want to put THAT MUCH effort and detail into the art), but there's no reason they couldn't do digitally-drawn art a la Muramasa, as you mentioned. Although obviously a much different drawing style would be needed for a Castlevania game. Though I fear they'd go for a very shiny, plasticky style, much like most current anime; the colors and lighting just look awful in most new anime I've seen clips of, and they sure like to blast the image with lots of really poor glare effect, but it seems to be the popular thing to do. Digital art doesn't have to look so artificial; you look at Miyazaki's more recent stuff, particularly Ponyo on the Cliff, and you see how traditional-looking his films are. It's a style, it's an aesthetic, and one a lot of people in the animation field don't really seem to hold on to these days.