I believe the way this should be implemented should be on their own continent(or something similar). And they should have an effect on ground-battles and be target able by ground vehicles.
On this new continent there should also be missile silo that can damage and take down one of these OAC. This being a persistent game would make missile silos valuable in such a way that they could potentially become key facilities. Also bases should be equipped with launch pods that allow defenders to board these OAC. This would potentially add a tactical layer as you choose between having them be a logistic ship or a combat ship by deciding to bring them close to bases.
Also land vehicles should not be spawn-able on these because it would take away from the importance of tech plants/towers.
Bane has talked about them having a maintenance cost and i propose one of the costs to these could be having it use resource when it fires it weapons. Another that was already brought up could be resource cost to spawning vehicles on top of normal vehicle spawn resource cost.
Anyways, sorry if its too long but this is my 2cents in implementing OAC
Edit: This was brought up in another thread
http://www.planetside-universe.com/s...t=42403&page=2 .
What if it had little to no AA guns so that it would have to rely on escort Fighters for defence? This could potentially make it something that outfits could specialize in/ cause co-operation of outfits.