As it stands, we have very little in the way of stances when it comes to concealment. A crouch would not only be ideal for keeping a lower in-game profile, it could also provide the function of softening your footsteps to lower detection rates on NPC animals, or keep players from hearing your approach. Ranged and melee attacks are possible when crouching.
Proning could be almost dead silent and drastically lower the detection rate of NPC fauna, but the player would be required to rise to a stand ro a kneel to make any attacks.
This also adds a lot of utility to the game. By having crouching as a viable option, you can have formations such as a shield wall crouching to allow a row of archers behind them to fire over their heads while the shields provide protection to the archers against incoming missile attacks.