I suspect there would be a lot more happy QFF members.
And a lot of unhappy shareholders. That is not how yield management works. The biggest earner is the premium cabins - and they keep the fares high. If everybody knew that they would release all unsold seats at the last minute, a whole lot more people wouldn't pay, and would wait - with yields plummeting.
Consider an A380 flying SYD-LHR. There are 70 business seats. Average revenue if they can fill them is probably around $6,000 or so.
Lets assume they fill 50 of them - so $300,000.
As a Classic Reward, that will set you back 144,600 points plus some fuel fines. Let's assume fuel fines of $200, and to make things easy, QF "earn" at 1c per point. That makes a CR redemption worth around $1,650 to QF. Say they release 10 seats (over the whole time). They fly out with 10 seats empty (or perhaps occupied by upgrades). Total J revenue around $316,500.
Now assume that everybody knows if the seats don't sell, then they will be release as CR. Even assuming this behaviour drops sales only 20%, and they release all the seats as CR, that changes the total to 40 seats at $6,000 for $240,000 and 30 seats at $1,650 for $49,500 - total of around $290,000.
These figures are just rough estimates, but I expect the release of all unsold seats as available for CR would have a much more drastic impact than this.