Surely if there is A inventory, it's bookable? If I tell my TA to nab me an A seat what part of the system will prevent her doing it? (I would try it right away but it would mean re-issuing my ticket first and I'm not ready to do that yet.)

If true then it is pathetic. From what I can tell off the web site nothing about the QF A380 seat makes it seem superior to CX's new F seat and CX hasn't created a new class or stopped allowing their use on RTW tickets. And it will be quite a while before QF can guarantee that you will fly an A380 on any single route. What happens if you have an R ticket and there's a substitution or you change your flight date and get a 747?