China Eastern Airlines still has the green light to enter the oneworld alliance despite the fact that Singapore Airlines, a prominent member of rival alliance Star, recently bought a stake in the Shanghai-based carrier. oneworld's managing partner, John McCulloch, said, "China is an unusual market for this sort of activity. We are proceeding as before... I don't think it is going to complicate things." However, it's important to note that oneworld is making an exception to the rule here - usually, this sort of thing wouldn't be permitted. "But in China," said McCulloch, "we don't see it as a complication." The Chinese market is a crucial one, so oneworld is understandably willing to make an exception.
McCulloch also mentioned the example of Cathay Pacific, a oneworld member that has a share of Air China, which will be a Star Alliance partner. Cathay subsidiary Dragonair is expected to join oneworld as an affiliate member, and Hainan Airlines is also in talks with the alliance about joining.
Air China, China Eastern, and China Southern are the 'big three' Chinese carriers, and each of them are now (or will be) part of an alliance: Star, oneworld, and SkyTeam, respectively.