The image needs some additional notes.
1) Two upper rails are for combinations of two devices:
- a daylight scope + night vision addon,
- a reflex sight + magnifying scope,
- a reflex sight + IR laser mounted on top in front of it,
- also it could be possible to have a reflex sight mounted on the front rail, for compatibility with NV goggles.
2) A large thermal scope could use both upper rails at the same time.
3) Basically, the front lower rail is for bipods and the aft lower rain is for foregrips, so it's possible to have them both at the same time.
4) A grenade launcher would occupy both lower rails at the same time.
5) Side rails are for additional small gear, like lasers, flashlights, maybe a camo netting attachment (sniper/spotter rifles)?
6) This is an example of a fully moddable rifle. On less advanced weapons, the slots could be disabled with an X mark, instead of attachment point icon.
7) AT launcher would work in the same way, as it works now.