Metro Trains Melbourne route (Craigieburn line, Sunbury line etc.) with the fleet of trains such as the Comeng train, Siemens Nexas train and possibly even a Hitachi train
Biggest problem with anything Australian is whether DTG have any associates down under they can partner with to do the research and liase with the train and infrastructure operators, if they are prepared to co-operate. Australia is a long way from the UK to send someone on a field trip and am fairly certain still subject to severe restrictions on people visiting due to Covid, which has no end in sight. As I understand it, people can’t even travel between certain States at present.