Can we have additional (preferrably moddable) characteristic for the weapon — cooldown time?
When you take a vehicle on the battlefield, there aren't much choices to take. You see the target — you shoot your cannon. Usually there's no drawbacks except for the ammo, and AP cost has its borders, since you can't take more AP for firing than the vehicle total AP capacity. Usually it's one-two shots per turn depending on weapon.
Adding the cooldown will allow to expand that border over several turns, possibly allowing to balance realistic heavy-damage weapons and compensating the lack of clip reloading mechanic in the vehicles. The player will get additional choice: shoot main caliber or save it in case of the heavily armored or safely covered target will appear, relying on different means to destroy current enemy. After the firing, again, you will have to decide leaving your tank as a cover, while it's unable to fire, or retreat for a time of reloading/cooling.
Also this will seriously benefit modders, especially alternate vehicle weapons like Max's Grease Pit. If the cooldown characteristic will be appliable on any weapon, it will allow infantry to use otherwise unbalanceable weapons too (It will further expand reloading AP cost balancier).
Alien AI can react to shooting from such weapon as the opportunity window to counterattack on weakened team, and so on.
P.S.: You are probably already have this mechanics used with the psionic abilities, right? And wraith randomblinking can "benefit" from this too.