The important points are that:
1. Qantas does not have a fixed number of classic award seats that it releases, so there is no baseline against which to assess whether it is releasing more or fewer classic award seats.
2. Qantas has never claimed that it will keep the same number of classic reward seats on the same routes. It might shift all classic flight award seats to MEL-SYD and remove almost all of them entirely from international routes, especially in premium cabins, effectively devaluing international redemptions.
From the press coverage, I'm going to revise my prediction. It doesn't look like it will be multiple tiers, but instead one higher tier like SQ Advantage awards.
As hb suggests, I think you'll no longer be able to get international premium cabins at classic award levels after this change comes into effect, except for when a flight is looking completely empty and they throw some out a few weeks/months from departure.
I also think this could hurt platinum requests for release of classic award seats. They might make this new higher tier come from the same inventory that is needed to request the release of an award seat.