I have a feeling infiltrators will excel at combat at night.
That said, flashlights have been mentioned more than once. Obviously as a flashlight on a weapon is a huge positional giveaway, I think that if a flashlight on a weapon is pointed at you, the glare should be enough that can't really see the target, just like if someone shone a bright flashlight in your face while in the dark IRL.
So long range players would probably elect the night vision scope, while those involved in shorter-range combat would probably go with the flashlight and switch it on or off tactically.
Also, I think it's worth pointing out the difference between thermal vision, which could potentially be countered by some sort of thermal shielding, and night vision, which could be countered by a bright flashlight in the same manner as mentioned before. There may be night vision in-helmet, for example, while thermal vision is restricted to scopes.
I also want to throw laser pointer attachments into this as well... I'd like to see them function as they really do IRL and paint a visible dot on the target which can't be traced back to the weapon unless there is fog or dust in the air.