Who in Australasia has spare narrow body (A320s) and ATR72s right now (that isn't in administration)...
Qantas wouldn't get ACCC approval.
Virgin/Tiger obviously don't have the money.
Alliance could swoop in, but they are quite well placed to start up this venture without REX as a partner.
I would be EXTREMELY surprised if Air New Zealand didn't step into this whole in the market. They have spare capital, spare aircraft, spare pilots and simulators for training - and they have been very public this year about their desire to extend their reach within the Australasian regional market.