I think it will only happen if AA/CX is awarded anti-trust immunity. Last I heard here, it looks in favor of AA/CX, but I am not the one to ask.
Knowing AA though, they will probably let Cathay operate the new route as they need to expand the alliance out of LAX and into ORD or DFW where there are more AA flights and frequent fliers.
As for what destination, that is anybody's guess. Last I knew, United was flying a 744 between Chicago and Hong Kong so AA/CX might want to go to Chicago and compete with them, or they could go to an untapped market in DFW and take 100% of the pax there, and let United take 100% of the Chicago pax.
Give me a break, I created this username when I was a kid...