Add the branch to Canberra and this, I think, falls within the range of a normal Train Simulator release. A route to Perth on the other end can be done in the future, perhaps.
Got any more details about the route like pictures, types of rolling stock used on the route, videos, those sort of things?
This might help. Turns out there are two main routes involved. One is the Main South Railway Line which begins (see the first link) at Lidcombe, which is at the top of the route here and goes 672 km (418 m) to Albury. The other is the North East Railway Line, which goes 352 km (219 m) from Albury to the Southern Cross City Loop. The extreme edges of the corridor are from Sydney to Lidcombe and from the Southern Cross Loop past Tottenham Yard and into Melbourne. So naturally, this is way too long for one DLC, but perhaps the latter of the two main lines into Melbourne can be tackled in one go with the other split into separate segments, each required to be added to the others to complete the full run over time. Each segment can extend the original line with the first being a prerequisite for use so that route merging itself is not necessary in the Workshop, as we would with the full line get a lot more use out of having the full kine. The only issue with using the full line at once is that it's apparently an 11 hour drive, so for scenario loading purposes, it might make sense to keep it in segments anyway. As for the train, the first link shows you: it's the New South Wales XPT, a diesel electric capable of 100 MPH (160 km/h). It runs in sets of four to six cars with 1,492 watts per powercar, and at one time ran up to seven-car formations. They can run in sleeper formation as well.
I would love to see a Sydney route developed. Hornsby to Katoomba; Bondi Junction to Cronella; Sydney to Newcastle and Sydney to Kiama. These would give great appeal both to Sydney and their wonderful railway network but would also enhance Train Simulator and TSW2
