So my buddy and I have been testing a bit and we did find one way FCs work with Powerplay. After seeing reports that it might be possible to use the cargo transfer tool to store PP Cargo (in my case, we tried with Aisling Programme Materials) in the carrier, we wanted to test and see how it works.
Fleet Carrier Owners can transfer PP cargo from their ships directly into the FC's storage using the Transfer button on the right hand cargo tab of your ship's UI. They can then move the carrier, transfer that cargo back out of storage, and deliver it to the desired location. In our testing, only the Fleet Carrier Owner could do this unless there is some setting in the carrier management we missed that would allow any player to load or offload their cargo.
What are the implications? Well, deep pocketed commanders from powers that use hauling (My own AD being a prime example) can use carriers to move large amounts of mats all at once. Granted, because only one commander has access to this transfer feature, the owner, it is probably a slow process of loading and unloading. Moreover, we at AD routinely have to race a sabotage prep hauling 100-150 thousand merits. 25k from a fleet carrier is not exactly a game changer, especially if loading and unloading are slow. But what about powers that don't typically compete with that volume? A sudden 25k being unloaded to some far out system in the last few hours of a cycle could be disastrous. Moreover, combat powers will not have similar capabilities.
Please disseminate this information to PP leadership in your respective powers, as we should all be aware of this capability and aim to study its potential for abuse.