the selling point is the new content; always has been. without blood elves or draenei, everyone woulda flocked to TBC. without DKs, everyone woulda flocked to Wrath. without worgens or goblins, everyone woulda bought Cata. even if pandaren were not playable and monks weren't added, everyone woulda migrated to MoP as well.
blizzard don't need fancy gimmicks to sell their product. the gimmicks are nice, but ultimately, people buy the xpacs because they're tired of the old one, not because they can be kungfu pandas.