Depots and cargo with a destination for space platforms, on top of the vanilla 2.1 platform-to-platform transfers. Mark a request group as reserve, cargo for chosen planets or a depot for chosen orbits right in the hub panel: reserve is never given away, cargo is held until its destination, a depot serves other platforms in its orbits. Supply lines keep one item list for a whole chain of depots, shuttles and landing pads.
Providing the player with new tools or adjusting the game interface, without fundamentally changing gameplay.