Yes, its Tian Xia, and its a part of Golarian. Both Ultimate books being published this year are supposed to have elements of that setting in those books as well. So the publication will be spread over all of 2011.
Sorry, I keep bringing up
Kaidan, but of course it too is an oriental setting for Pathfinder. Since Rite Publishing is also aware of this schedule, the current development of Kaidan is geared to be released before any of Paizo's oriental aspects do so. We want to have the first PF oriental setting and ruleset among the various publishers for PF, including Paizo itself.
While the classes are being built for Kaidan (mostly archetypes of standard PF classes), any new classes that come from the Ultimate books, the Tian Xia setting book and whatever else is released by Paizo, should be completely usable in Kaidan itself. Barring specific setting rules that might require Paizo material tweaks to better fit the Kaidan setting.
I am working hard to make Kaidan feel like the far east, in more ways than language, culture, magic and samurai - what I would expect from any other oriental supplemental publication. Life, death and reincarnation, animistic spirit/deities, ancestral magic, a different kind of undead - all this is intended to give an oriental feel that other settings just won't be able to capture.
I know Kaidan will be great, I just hope it and Tian Xia will be able to mesh well. Kaidan is an archipelago of islands off the continental coast, so it should be able to plug-and-play into any existing setting, Golarian included.
GP