For this question, you need to ignore the fact that passenger rail services are generally not financially viable on their own and they need to be subsidised.
Basically, my question is whether there is anything legal stopping the two main regional passenger operators, NSW Trains and VLine, from operating in other states. Eg, could NSW Trains operate its own services say Albury to Melbourne (in addition to the XPT that already does that). Could VLine operate services into NSW? Could either of these operate services elsewhere (Qld, SA etc) without any legal restriction? I know there would be requirement to become appropriately accredited and comply with the track access requirements of the networks they operate, but my question is more around if there are any legislative restrictions on competition in the relevant states. Or is it open access to all?