I hope that refueling fleet carriers uses actual fuel, albeit a LOT of fuel. Think of it - we could become 'oil tankers' in Elite! I can picture my Type-7 (love that ship) loaded with extra fuel tanks and a huge scoop, loading up on fuel at the local star, ferrying it to the fleet carrier, rinse and repeat. I suppose one could buy fuel at the station as well. Perhaps with the run on fuel, Frontier could raise 'gas' prices to match accordingly.
While this may sound dull to some, I think it beats having to harvest jumponium or something... Though you could add a cool mechanic to allow greater jump range based on fuel type and synthesis. Imagine harvesting neutron stars for greater FC jump range!
Anyway, for the sake of immersion and "fun" (I actually would enjoy ferrying fuel), I hope Frontier considers this option. Thoughts?
ps - This assumes FCs need refueling to begin with. I'm not sure the lore behind megaships not being able to scoop their own fuel. Too large for the gravity well, perhaps?