Also, with a day/night cycle there would need to be extra locations so every NPC had a bed at night, extra work filling in those locations with decoration, loot, quests and things to find while exploring, the actual NPC scripting to react to the day/night schedule, much more dialogue so NPCs can adjust their speech according to the situations, extra complexity with the reputation system so waking someone up to solve a minor quest or buy one potion is different than those actions in the daytime, extra opponents and quests that take advantage of the cycle, enemy scripting to change encounters between night and day, extra balancing work for all the differences added due to the cycle, additions or changes to the skill system based on the time of day, extra QA time testing the many different quest paths and combat encounters, etc.
Not to mention, that such changes could impact quest or even major storyline... or even a personality-change(if the game implements that) and so on... :p
Like for example: assassination or infiltration by Black Ring or some other party?
Or even: spells which can change day/night cycle, for certain effects when combined with other spells...
Man, I can see a massive headache coming on. :p
