We've hit on the topic of "classic" servers before, and there are even players already carrying the idea out in game. Not everybody thinks Burning Crusade is the greatest thing since Molten Core, and so there are still quite a few players who wish they could play on servers that didn't go past level 60, where Naxx and AQ were still the main endgame, Bloodfang was the hotness, and Atiesh was more than just a few splinters taped together.
But while people have asked for classic servers before, Drysc repeats what some of them might not already know: that though Blizzard has "seriously" considered the idea before, they eventually determined that it would be too much to run two majorly different versions of the game at a time.
It's worth stating that you can definitely still run vanilla WoW without installing Burning Crusade at all, but even if you do that, you'll still see Blood Elves and Jewelcrafters running around, and people in the battlegrounds at level 60 will probably trounce you with all of their shiny Outland gear. It might be nice to experience the old endgame the way its meant to be experienced, but at least until WoW's population slows down and Blizzard determines they have the resources to do so, you can't go back to Old Azeroth again.