The 737's are beginning to get old. Carla had some psychosis induced vision to order a "butt load" of A320 family for asian entities, and the former LS had stated changing gauge for short haul could occur around 2017 (when swapping from B to A is an option). To be fair he was explaining at the time why it was too late to order 777's, so maybe it was all lies.
Yep, it would cost money to retrain, however the decision would be factoring fleet renewal of the earliest -800's vs NEO's. Think new capabilities of new versus keeping the status quo...
Personally, I'd think A320's for JQ and QF makes heaps and heaps of sense, and therefore won't happen.