Even trying to provide for members can be difficult and that difficulty ramps up the busier the fc is and the more members it has. Fighting with requests, the huge time the trips can take, as well as the random nature of loot on top of that - it can potentially take weeks just to fulfill one small request if you've got bad luck. All the while more requests pile on and people start getting aggrivated that you're showing favoritism to person A whom you're just trying to get one item for before moving down a list. Even if it requires being in an fc to use, I would love to let people have access to their own airship/sub. In fact why not make them character locked so buying extra houses doesn't net you additional submarines/airships?
