Tobold has another post up that piqued my curiosity. He disdains the possibility of classic raiding guilds (apparently not aware that there are at least a couple classic guilds out there that refuse purchase of TBC or WotLK). He's probably right that the vast majority of players aren't very interested in raids where you don't get the latest and greatest gear.
However, I think he discounts the power of nostalgia and history too much. Lots of people enjoy going into those old world raids (like me--I still have yet to make it into the Sunwell, to my eternal dismay). One of the interesting properties of WoW's constant updates is that raids and zones are systematically discarded, and the bleeding-edge population moves on, leaving the old zone basically empty. But my feeling poking around the old raids was the powerful pull of historical curiosity--I wanted to know what the classic raids were like, how the bosses worked, etc. And I had a great time doing it. The constant updating leaves multiple layers of old content around, which gives WoW a historical punch far outweighing its five-year history.
In short, I think there is a market out there for this kind of old-world exploration, and it's definitely worth an second look for Blizzard.