Must be an election coming. This has been well studied, I was involved in the study 16 years ago.
There is no corridor to extend past Mandurah, you would have to come off at Lakelands and run round the road corridor.
Might be of interest to you as this potential project seems to be gathering some steam.....Project Coordinator position
"As a senior member of the Infrastructure Planning & Land Services Division (IPLS), in this position, you will play a leading role in the development of concepts and proposals to produce definitions, costings and evaluations of options for major transport initiatives. This role is specifically to lead the development of a strategic business case for a fast rail connection between Perth and the Southwest region of WA.
The concept of a fast rail connection between Perth and Bunbury has been considered for some years. Following recent commitments in both the Federal and State Budgets, IPLS is resourced and mandated to work with the National Faster Rail Authority to investigate whether there is a case for such a connection, and if so, the population, development, and economic circumstances in which it would be justified. Pending the outcomes of the strategic business case this position will also lead the process of using suitable mechanisms to secure the land required to enable the infrastructure to be constructed in the future. This is a high-value planning project with strong stakeholder interest"