Well, that's sort of what already happens. It just happens to be backwards.Seems pretty clear the ships are more chartered under various terms then picking up spot market lots, otherwise they are doing speculative too.
Rather than picking up a lot with a set destination, you pick a destination and see what lots are available. The former wouldn't be super hard. Just roll on the same table for all the "nearby" ports.
Mind this is where "per parsec" pricing would shine. There has to either be a fixed rate (like now, 1000Cr per ton), or a "willing to pay" rate associated with the lot.
This is important because if a generated lot is given an amount willing to pay AND a time to be delivered, a ship could, for example, pick up two lots. One for System A and one for System B, assuming that the the B lot says "must be delivered within 3 weeks" or whatever.
I think this could be a much more dynamic system outside of speculation.