I fully understand your frustration. However, I think it's really hard to ask CX to transfer you to a QF J class if you are really paying the Y class fare at that point of time. Though your theory may be right: you use your points to upgrade to J class, then you should be entitled to be a true J class passenger. This theory should only be feasible when you are travelling CX flights. However, if CX needs to transfer u to another airline (no matter ow or not), they have to pay that airline the price of the ticket (though they may have some inter-airline discount). The problem pops up here. If they transfer u to a QF J class, they have to pay QF J class fare, the cost is far more expensive to them than just upgrade u to their own J class or even F class.

I think the CX and the QF staff, especially those in HK, won't care too much if you are holding a CP emerald plat card if their flights are totally full or in this air pilot 'sickness' situation.

One thing that you can do is to become the CX Marco Polo Gold or Diamond, they may give u a kiss at the gate!