I think they could even out the balance between the the player occupations - lessening the importance of the pilot. Especially if you use fighters (which makes the pilot class very useful).

I suggest a maximum of 1 turret for sizes 5-8 and 2 turrets for 9&10.

The turret being a completely internal module that must be located in the bulkiest portion of the ship because of the mechanics needed to move it.

The turret behaves exactly like a cannon but only has one side arc of fire. A player operating the battlestation for the turret may rotate the turret to any other angle as an action.

Use an Hyperdrive module to represent the turret. Rotate the module whenever the turret is rotated such that the open end faces away from the direction of fire.

For the purposes of module limits, a turret module counts as a cannon module (ie you can have a maximum of 4 modules whether some are regular cannons or some are turrets).

When I design the art for the turret, I will have the turret separate from the module housing it - because it is the part that rotates, not the entire module.