scooter guy we would be wise to stick to the facts about these trains, they are bizarre enough without the wild speculation you have provided.
As for your suggested destinations, consider the population growth of those centres needed to justify extension of the rail. In fact Seaford should never have been done, only 10% of commuting and related journeys leaving Seaford end at places connected to the rail service. See my rants elsewhere about the CBD and its declining focus.
Think also about the irreversible changes to the Barossa Valley if the population was allowed to grow to the extend needed to support a viable rail service.
Consider also the loss of SA's best cropping country if Hamley Bridge, Balaklava and Kapunda were also allowed to develop. These places could in days of yore just sustain* a Brill railcar service at a one or two trains a day basis, Kapunda about 4 trains a day. * note I didn't say justify.