My understanding of the Perth base for 73's is that it will pretty much be filled entirely by our much under utilized brothers from the e-jet. With no plan to replace the drivers who go as there is an oversupply of pilots on the e-jet anyway.
Bright side is that it is reducing the number of surplus guys in the system, so hopefully there might be some external recruitment in a few months.
My guess is the the 73 base in Perth will only be 2 x 737-700. At least for the short to medium term.