Things Blizzard could do with a Proper Day/Night Cycle in WoW
Make forests like Duskwood and Silverpine really frightening.Have unique visual effects for various classes really pop: moonlight from druidic spells etc.Make critters and monsters active at different hours, so for example at night you might expect to find more fireflies and spiders, by day rabbits and sheep.Have light sources like bonfires, torches, and lit windows be really immersive at night.Bathe zones like The Barrens in moonlight.Have unique-looking herbs, like Silverleaf, glow in the dark.Implement torches and other mobile light sources.Turn cities into living places, as the cock crows in the morning and traders begin pouring in from the countryside with fresh produce, or when the taverns play music at night and certain NPCs visit the bars.Unique nightly events that you might stumble on, such as a secret cult meeting in the middle of nowhere, or a wild worgen roaming the countryside.Make various racial abilities really cool; Night Elves' Shadowmeld could be more potent by night, while Tauren might be emboldened and gain Stamina by the light of day.List goes on. Some of this could be achieved already, but it'd be a lot more effective with a proper day/night cycle with dark nights and really clear sunrises and sunsets.