I for one am looking forward to seeing R766 steam onto Roma Street with a train of blue and gold Spirit cars, turning it would probably involve splinting the engine and tender and I am sure there would be no problems getting bums on seats for a Roma Street to Southern Cross trip.I can well understand this. It would be fantastic.
Some factors to consider are:-
Spirit cars are on BG. Who is going to put them all on SG, and who's paying?
They are sitting cars - do you really want to sit up all the way from Brisbane to Melbourne?
There will be a limit on the number of cars simply due to the hauling capability of the R. Off the top of the head, seven vehicles would probably be a fair load. Amongst these vehicles will be a power van, and another van for carrying engine requirements et al, plus at least one buffet or diner. This obviously affects the number of passengers, and would inevitably result in a pretty expensive trip.
Where will the loco take coal? How will the coal get there? If it carries its own, bang goes more seating capacity. Same with water; hauling a water gin equals same result - even fewer bums on seats.
Everyone is going to be pretty smelly by the time they get to Melbourne; there are no showers on board.
Will there be enough loco crews to cover such a distance? What about train staff? They'll probably require a crew car.
Splitting the engine and tender sounds fine, but have you ever done it with an engine that has a mechanical stoker? It's a much more fiddly job than normal.
I love enthusiasm, but unfortunately it has to be matched with practicality.