More info here: (own work) From Sydney Central Station to Katoomba, Australia. Could include the City Circle. Many suburban services between Central and Emu Plains, and regional/intercity extends up the steep incline through the blue mountains. Fairly slow route, top speed around 130km/h. Rolling stock could include the Sydney Trains A set and NSW TrainLink V set.
Great video! Love the details. The Blue Mountain Line is a popular one! Just a correction; Sydney to Parramatta wasn't the first railway to open in Australia, that was the Port Melbourne railway line. Sydney to Paramatta was the first to open in the region that would become the state of New South Wales though. I've added it to the list of Australian proposals found here: https://forums.dovetailgames.com/threads/australian-proposal-suggestion-master-list.41526/
Nothing west of Parra will go around the City Circle (none of the Intercity lines do at all), so to include it this would really need to be a hybrid between the NSW Trainlink Blue Mountains line (V-sets running between Lithgow and Central and the odd H-set/OSCAR) and the Sydney Trains T2 Inner West line (A-sets/Waratahs running from Parramatta to City Circle). To get non-Trainlink services between Emu Plains and Parramatta you'd need to incorporate the T1 North Shore and Western line, but that too doesn't go around the Circle so would need to terminate at Central (and cut out the North Shore part) EDIT: After watching the video, I see that this is mostly covered. Although in parallel to the "not Australia's oldest railway" comment above, the Blue Mountains line also isn't Australia's highest railway, as the Skitube Alpine Railway at Perisher is a good 900m higher.
True, still only gives a portion of the City Circle though and would be a rather arbitrary ending point as none of the current timetable Emu Plains/Penrith services terminate there - might as well extend to North Sydney and have the landmark feature of crossing the Harbour Bridge