Something like an A220 would break Rex very quickly.
If AJ were actually inclined towards buying anything for QF, I could see them being used to replace the 717s. Beyond that though, I don't see it being used in regional Australia.
Populations...Wagga is about half the size of the combined Albury/Wodonga. Flights to Melbourne are only done by Rex, and I wouldn't put the overall load factor at much above 50%. Whilst the train service isn't wonderful, it's pretty cheap, and it's an easy drive. Sydney is out of casual driving range, and so it sees much more demand. There's quite a large contingent of military passengers on the flights. Remove them from the equation, and you could probably remove one of the airlines.
There was a jet service to Qld, but it didn't last long. If I were a skier in Brisbane, I'd go to NZ.