I have not been following the Australian proposal, but general freight and mixed passenger/freight is carried on high speed rail networks in other countries. A passenger only high speed network in Australia would not be viable due to our relatively small population and long distances.
A recent ABC article I heard on the proposal - which gave me the above statistics - talked of passengers and general freight.
And if they can reduce the number of Toll, TNT, Linfox, Australia Post, Q Rail etc roadtrains on our highways, it would be a blessing to motorists and enhance road safety.
But I suspect $114 Billion for 1,748 kilometers of track is another wet dream, the same as variously $20 to $45 Billion for the NBN. The entire proposal should go no further until it is accurately costed and an honest cost/benefit survey carried out.