I personally hope that the ADS system is similar to that of borderlands, where it allows you to center your aiming on a target, but does not actually increase accuracy compared to hip firing.
To simplify, it works like this: when you hip fire and when you aim down sight you have an almost identical amount of spread, but using the sights makes it easier to focus that spread towards a single point.
English
-
i say this because i want hip fire, its not that I'm too lazy or unskillful, but in my opinion the only weapons that need ADS of any kind are precision weapons, like sniper rifles and semi-auto or burst fire assault rifles. Bungie has done this well so far with the halo series.