The newest BG loco's are now SG loco's in the form of the C classes and when all the murray basin lines are converted to SG do you really think that operators will want to take the longer route if a faster route can cost them less.
If a sleeper train were to be provided between Sydney & Melbourne, something along the lines of the Caledonian Sleeper would be the way to go. Full service, CBD to CBD utilising new, luxurious rollingstock running express at between 160 & 130km/h for most of the journey and running 6 days a week. It would need to leave Melbourne after 9:30pm and arrive in Sydney before 8am (and vice versa). Prices would need to be competitive with Airline Business Class fares.
This would not be possible with old Southern Aurora Rollingstock.
Of course, you could still call it Southern Aurora.
The Cs are not even remotely the most recent locos built for BG. There’s the Gs, the XRs, and the VLs, as Dan rightly points out, and of course, the magical thing about locos is that they can be gauge converted if and when the need arises.
As for the Murray Basin, I don’t even really know what you’re getting at; if the route doesn’t exist the operators won’t be clamouring for access.
Read what I said again: the major obstacle to further standardisation is entanglements with the metropolitan and commuter passenger network.
The C Classes were the first turbo-charged loco's and were introduced during the Hamer (Liberal) government in the mid 1970's. Moreover at the time because they were so heavy they were limited to 80Km/h on the SG to Albury.in the early 1980's there were 4 C's on 'the gauge' and 6 on the BG. The SG ones were consistently 501 to 504.
I remember one night behind the...'Southern Aurora' (so at least one of them was SG if I recall) the loco had no problems hauling the set up the Divide at Heathcote Jn and because of that, it was able to pick up some of the time lost between Spencer St and Wandong doing 80Km/h...however it lost time after Seymour and was a liability rather than a bonus on the run despite its turbo power, so it was only ever used on the 'Aurora when it was absolutely necessary.