Such armed container ships can also loiter and/or outright be stationary in the middle of the Bohai, Yellow, East and South China Seas. They could serve as forward pickets + SAM batteries that would extend China's SAM coverage into the sea from the Chinese shorelines, alongside serving as backup SAM batteries for the Chinese-held islands/atolls in the SCS.
Yes, I believe this is closely related to the JASSM/LRASM.
JASSM/LRASM uses a high-high-low trajectory, utilizing the Earth's curvature at the terminal stage to compress the detection and defense capabilities of ground-based SAM systems. PLAN needed specialized destroyer-frigate fleet to extended coastal air defense zones, but their VLS capacity was limited and vulnerability to LRASM strikes constrained their effectiveness.
These container ships, at least the anti air version, stripped of their anti-submarine and anti-ship capabilities, have taken on some of the nears sea air defense tasks, allowing more fleets to extend the defense perimeter further into the far seas.