Whatever it is, nobody's ever heard of it yet, if it's even been invented. The DVD format is pretty new. Nothing is going to replace it for a good solid while. Heck, it's going to be another half dozen years before DVD finishes pushing VHS out of the market. As near as I can tell, there are currently still more VHS players in North America than DVD players (although, I'm pretty sure at this point more movies are watched on DVD than VHS; people who don't have DVD yet tend to be people who watch relatively few movies). Frankly, most of the DVD players that have ever been sold were manufactured in the last two years, and for the moment practically everyone that has a DVD player _also_ still has a VHS player (although that is starting to change, gradually). Plus, cam corders still mostly use VHS. DVD burners for computers only became sanely affordable in the last year or so. In short, DVD has only just barely arrived. It's not going anywhere for at *least* a decade. Any attempt to market a successor format now is going to meet with widespread apathy if not outright disbelief and scorn. Well, outside certain very narrow niche markets, it will. There are of course always a handful of people who will seek out and adopt a format if it meets their special needs (e.g., Laserdisc, which was present in school film departments and media labs all over North America for _years_ while the rest of the world used VHS), but that sort of product isn't going to push out a mainstream format like DVD. A few videophiles may adopt this or that, but for most folks DVD is still going to be the "new" format for a nice little while yet. Talking about what's going to replace it is, in a word, premature.
HD-DVD and BluRay are competing for the niche markets formerly occupied by products like Laserdisc. Their proponents may *think* they're aiming to replace DVD, but that's a lot more enthusiastic than realistic.