No matter what they do, they're going to have some people screaming about the game being not "Their" version of Vanilla. 'Cause each person is going to have their own favorite parts of it. Will they allow the Pet-Plague to wipe out Orgrimmar and Stormwind, again? Doubtful. That's going to piss off some folks who enjoyed that. Or kiting raid bosses into major cities to cackle as the locals are slaughtered. No way -that- would make it live, again.
There's this, too, absolutely.
In any event, Classic WoW won't be just a cash grab aimed at 'Nilla Wafers. They're going to try to get as many people as possible buying and playing the game.