Since the ammo concept has now been firmly ingrained across multiple classes, if not all ,to some degree, then it could be implemented for turrets. Rather than having health they would now have an ammo count that reduces with each auto attack, with overcharge using up half of the total ammo. The turret would detonate once it reached zero ammo, with the tool kit able to replenish ammo (possibly even moving them via magnet pull as already suggested) and hard CC being able to further reduce the ammo count to enable counter play. I'd also look at adding turret upgrades to some of the existing traits across the trait lines so that it gives something core engi would be able to specialise in.