Here are the seat maps for those interested. https://www.qantas.com/au/en/qantas-experience/onboard/seat-maps.html
A bit of self research will show A320, Fokker100, some 717s and Dash 8 (of course) without business. I'm not sure Qantas would be flying a Dash8 MEL-BNE, but there is always the Dash 8 milk run from BNE to CNS. Not that you'd need to go economy MEL-BNE if they put you on the milk run...
E190s have fewer business seats.
So those are all good candidates for the new aircraft type.
A330 to 737 is also a possibility, I guess.
A bit of self research will show A320, Fokker100, some 717s and Dash 8 (of course) without business. I'm not sure Qantas would be flying a Dash8 MEL-BNE, but there is always the Dash 8 milk run from BNE to CNS. Not that you'd need to go economy MEL-BNE if they put you on the milk run...
E190s have fewer business seats.
So those are all good candidates for the new aircraft type.
A330 to 737 is also a possibility, I guess.