This is a common meme, but I think the CX-blocking-CZ thing is overblown here on FlyerTalk. While ambitions may be there, I really don't think they're competing for the same passengers in most cases; CX is mostly focused on HK O&D traffic and long haul transfer traffic, while CZ's business is mostly operating a gateway into the PRC. Sure, there's some overlap, particularly on Australia routes. But by and large, I don't think anyone is going to stop booking CX flights because CZ is suddenly an option that earns miles.

In fact, competition from CZ could be a reason CX's thinking is changing on the topic. CX is losing money hand over fist, and part of the problem is long haul competition (especially from Hong Kong Airlines). Bringing CZ into the OneWorld fold could open the gates to a bit of coordination so they don't step on each other's toes, and can focus instead on squeezing out HX and other low cost interlopers.

Remember, there are central planners for the aviation industry in China, and diversifying their three major airlines across the three major alliances has to be an attractive goal for them. While CX is still a Hong Kong airline and the Hong Kong aviation market is still free, they operate a lot of routes to the mainland, and there could certainly be some behind the scenes favors on offer to convince CX to cooperate if they really want to get China Southern into OneWorld.