737 vs A320:
One would imagine many inefficiencies during the changeover period if QF was to replace 737s with A320s.
There are 5 bases, and the oldest batch are around 14 years old vs the newest batch which are near new. So possibly many many years of a mixed fleet. The purchase price would have to have a pretty significant differential to justify the additional cost and loss of flexibility of a mixed fleet.
So, yes, they will probably do that.