I hate this kind of zooming.
One of the things I hate about the ArmA series. It makes the gameplay far less smooth.
I am ok with
fixed iron sight zooming, but I don't like zooming out of iron sights with variable levels of zoom for a few reasons.
1) If you are running (usually not zoomed in), then someone who is standing using this zoom feature can see you from a distance much more easily.
2) It looks and feels awkward.
Typically, this means that you hear a bullet go by, but can not see anything... until you use the zoom feature. This just breaks the immersion and feels awkward.
Iron sight zoom may have its advantages, but I don't see the point of a non-ironsight zoom. No matter what is done, I'll still be staring at a 19" computer monitor. Some things just can't be modeled realistically in games.
That being said it will be in the game so there is no reason to discuss it further.
I think ArmA handles it pretty well.
One of the most annoying aspects of the series IMO.
But if it has to be in, then ArmA's button set up might be the best solution.