Okay so, I'm not sure if this was already suggested, I used search and found nothing like this, but I may have done it wrong =P
Anyway, the idea is: Depending on the weapon, the zoom when you aim down sights changes.
Shotgun is more of a short range weapon, so it should have no zoom or really little zoom.
SMG is more of an mediun range weapon, so it should have some more zoom, but not as much as Rifle. Something between Semi and Shotgun.
Semi Rifle should have the higher zoom. I guess the one we have on this version is just fine.