For a while, it'll be about 3 routes (SYD-MEL, SYD-BNE, BNE-MEL).
Most people earn Velocity or Qantas points to travel on holidays (often long haul) so unless it's great value with lots of ways to earn/redeem then I can't see many people making the switch. Besides Qantas has got Woolworths and Virgin's got Coles, where does this leave REX IGA or Aldi?
I think everyone is missing my point. I'll often search google flights and sometimes Webjet/Expedia before booking and if it's showing (incorrectly) that REX is more expensive than Virgin/Qantas then most people aren't going to even bother looking any further or even consider REX as an option.
The other big thing that people are missing is that Flight Centre still has corporate contracts through FCM travel with many companies opting for a best fare of the day policy (however most exclude Jetstar). Again despite REX in theory having cheaper fares directly on their site, as the travel agents are seeing more expensive fares REX is less likely to be booked under any travel policy.