From my morning dialogs:
The Taiwanese activists shipping out to the Senkaku Islands are by themselves a relatively harmless sideshow. However, the Chinese response to it might not be. The Chinese authorities may exert authority over it by 1) apprehending it or 2) protecting it from the Japanese authorities. Protection is the more likely of the two, since (according to my recollection) the Chinese government has been encouraging towards such Taiwanese efforts. Either way, such action would be a new step in Chinese escalation.