parabellum,
Think its a matter of public record that over years QF has had discussions with SQ, MH, CX about things from mergers to codeshares etc but never been able to come to an arrangement.
On the codeshare front, SQ is much like CX... They don't really need Australian connections as they fly into every major port, and why help QF out by giving them a codeshare out of SIN/HKG, when you can just say no and funnel more traffic onto your own metal.