Tycho over at Penny Arcade speculated a few weeks back that Blizzard’s new MMO project will simply be an engine update for WoW, but I don’t think this will be the case. It seems inevitable that someone will eventually come out with something better designed, more accessible, more fun than WoW, just as WoW did the same for Everquest. And of course Blizzard would like that “someone” to be them.
I’m also not convinced that “the next big game” will be significantly more advanced than WoW, graphically. When you get into the sort of subscriber numbers that WoW has, you’re reaching far beyond the market segment of hardcore gamers, which means you’re targeting people that don’t make a point of upgrading their PC every 2-3 years. So you’ve got hardware limitations to deal with.
I’m also of the opinion that graphics technology today is already “good enough.” It can (and will) continue to get better, sure, but the main thing that distinguishes WoW for me visually is not the graphics technology, it’s the aesthetic. The art, the architecture, the style and spirit that goes into the world is something I find beautiful. I think it’s wonderful that graphics technology is advanced enough so that artistic beauty is finally the biggest differentiator in terms of a game’s visual impact.