For now only some weapons allow to make single aimed shot. With my proposal there would be separate "aim" action. It should take some time — as much as takan on existing aimed fire modes comparing with single snap shots.
This would be great when used with long queues from e.g., heavy machinegun and needler. And very necessary for plasma blaster! (if with machinegun at least some bullets hit anyway, what is acceptable for weak enimies, which currently are only available target for machinegunner, but with blaster it is like "Die or live", what is reason to not use it, unlike plasma rifle).

Some weapons are known to have bipods, which may be better aiming mode. There some cases, where it should be available:
1. Player hides seating behind low obstakle like barrel, which allowes you to shoot while enemy can't (but can when you stay).
2. Laying on ground (would be third mode in addition to sitting).

More words about laying mode follows.