“On its own, a joint exercise among claimants in disputed waters would mark an important development in regional relations,” said Jonathan Spangler, director of the South China Sea Think Tank in Taipei.

But improvement of broader relations would take longer, he said. “It all depends whether or not China and ASEAN can keep up the positive momentum,” Spangler said. “Because the underlying disputes have not been resolved yet, that may prove difficult in the long run.”