Religion and beliefs were always part of warcraft races, it plays a major part of societies present in warcraft universe.
humans worship the light, while night elves worship elune, tauren worship the earthmother, orcs look up to their ancestors for guidance, the forsaken have their own religion.
some races have similar beliefs (like dwarf and human paladins, both worship the light) and such.
so with this in mind, would you like to see a minor system implemented that lets you choose a religion, becoming the follower of that certain religion requires you to visit the temples of the chosen religion and will unlock questlines and dailies which revolve around that religion's customs. this will allow the devs to introduce a deeper understanding of each religion to players.
rewards can also be put in place for these religions, to encourage players to increase their reputation with their temple.
EDIT : perhaps some spells and abilities can also be given to those who have reached the highest rank in their religion.