Having been a United Premier Gold refugee from them moving from an entirely BIS (butt in seat) elite program to now a mostly $$$ based program, I think moving the program over to entirely $$$ spend will turn a lot of people off. It's one thing if they offer an option to members to attain status based on spend whilst retaining the existing quasi-distance based status credit system. After all, there probably are a certain portion of members who spend thousands or even tens of thousands on short haul flights on Qantas but have little to show for it given the lack of recognition for spend.
However, moving to a loyalty system based strictly on spend will cause travel behaviour Qantas probably isn't expecting. After all, if you have to spend tens of thousands to get any meaningful recognition on Qantas, then why bother remaining loyal to them? Why not get all the benefits (and then some) of elite status by flying business class on whichever carrier has the best price, schedule and service (here's a hint: Qantas rarely wins on those categories)? The other concern I have is it would send a strong signal to Qantas elites not to fly Qantas on international trips. After all, why fly Qantas whose elite status accrual is based on spend whereas flying AA or British Airways it'll be based on distance again. Remember every carrier that has moved to a $$$ based system for elite status be it United, Delta or AC have carve outs for their partners because they cannot know how much you spend with their partners. For instance, it is well known for United's elite status that discount business (P) fares on a partner like Air Canada can be a very lucrative way of earning status with United.
-RooFlyer88