That's interesting. The ultimate goal I'm presuming is a way for the player to "kickstart" a new colony's stockpiles with supplies, without having to go and collect supplies themselves, but at the cost of additional credits (convenience = expense). Or perhaps for the player to get a whole lot of supplies to an outworld colony if they're running low, and don't want to trek back to the core worlds themselves.
I imagine it implemented as a dialogue option at a station you control, perhaps requiring the "Waystation" industry/structure. You hit "Request supply delivery here" in the dialogue menu, which would have a credit cost associated with it, and a fleet is generated somewhere within the core worlds and travels to the station. Once it arrives, it performs just like a merchant fleet, it hangs around for a bit and unloads a bunch of supplies (maybe some fuel too and other stuff) at the station for you to grab.
I can see a lot of possibilities here for world interactions too, such as pirate fleets being able to intercept this resupply fleet. That said, that would undermine the concept of the "convenience" factor (ie. the player not needing to be involved), so it would require careful thinking about. Also, hehe, imagine if hostile factions could sabotage the supply fleet.