While I'm sure this feature has already been planned, I would like to take it one step further by sharing the work I have done on it.
The basic idea is to add a "wild" variation to chickens which I suggest should be a bird, like a quail (or similar).
Here is a model that I created in blender and while it is definitely a work in progress, I believe it is a very good starting point if you go ahead with my suggestion. (And yes, I know the face is very derpy but Gruk can probably fix it)
Why a Quail (or similar)
Quails are found in many places on Earth so transitioning this to the mod will allow this mob to logically be found in nearly any region.
Quails are perhaps slightly small for mob but since it's Minecraft, could be sized up to better interact with the world. Another solution is to use another bird type like a spurfowl or other similar bird.
These mobs could have the same behaviour as chickens. (floating down, ground-dwelling, egg-laying...)
Other items to go alongside this mob
Raw Quail meat which can be cooked
Quail egg which can be used alternative to a chicken egg
Finally, here is the work in progress files including the .blend, .png texture and a screenshot of the mob.