The main issue i could see with doing Australian locos was our different track gauge in different states, although standard NSWGR stuff would be perfectly suited to the track in game, it would probably be a good jumping off point to do narrow and broad gauge track mods to add.

I personally would love to build a railway based on Queensland Government Railways, with the appropriate stock and motive power etc (and stations and structures) but as yet such a mod is too 'niche' and likely not be seen for a long time, if at all

would be nice if it can be done would love to run double heading garrets on a freight line
and a 36 class with a 38 for passenger