Collaboration confirmed. It's called I'm Not Yours and is Jolin's first attempt at composing.
Lyrics are a mix of Chinese and English, and Namie sings a bit in Chinese. Namie said "If the Taiwanese fans like it, I'll be happy".
The song has not been announced in Jolin's PLAY tracklist so I wonder if this might be a hidden track or will be in a repackage.
There's also a Celebration concert scheduled for December 7th where Jolin will sing every song from PLAY.