"3. Freight - connected to southern part of country by rail."
any freight that comes in via aircraft is high value, time dependent compared to (say) cars.
You're suggesting it be off loaded in Darwin, trucked over to the rail-yard and then spend a day or so on a train to Adelaide? From where it has to be repacked or sent on somewhere else.
I don't think that works.............
I am thinking exports rather than imports.
Agricultural products from rural Australia up to Darwin by rail and then freight up to Asian markets.
We can do it with lobster from Tasmania.
Why not premium agricultural products from rural Australia