Konami has *always* been very generous with Castlevania. You can find Castlevania on pretty much every major system to date (and a lot of non major ones). Here's the list: MSX, NES, Commodore 64, Amiga, Arcade, Gameboy, SNES, TG16, X68000, PSX, Saturn, N64, GBA, PS2 and a cancelled Dreamcast game. The only notable systems missing from the list are the latest ones (GameCube and XBox). However, the DS being primarily a 2d system (count on it) I think we can expect a Castlevania game.
Unlike GBA/GCN connectivity which requires two systems and can be a real pain in the ass, I can really see a lot of developers being excited about working on this system. That would be good.
I can almost see another two castle game (like HoD) with one castle on one screen and one on the other. As for what gameplay purposes that would serve... I'll leave that up to IGA (but the possibilities are enormous (though some of my ideas are admittedly ridiculous and unplayable).
I think this will be a cool system.