For every player who adores leveling alts lies another player who lives only for endgame content. These are the players who methodically prepare for patches and expansions long before they arrive. They stockpile points for gear and materials for crafting. They play through content during beta testing to get the lowdown on as many details as possible before attacking it on live. These players farmed the Timeless Isle dry before the time itself even had time to dry.
And unless these players are constrained by a raiding schedule that's less frequent or successful as they'd like, once they've devoured what's available at the endgame, they become bored. Undeniably, utterly, irrevocably bored.
If endgame-only is your preferred playstyle, have you already gone largely or completely inactive for Mists of Pandaria? Have you been successful at finding something else in the game to tide you over until the next bit of new content? If you do stop playing once you've gobbled up whatever's new for endgame players, do you chomp impatiently at the bit for the next release of content -- or are you always vaguely anxious that there might not be enough to tempt you back again?