I'm not going to criticize the casting until we learn what the rationale was; and I do agree on the surface, it does appear to be an "unfinished business" type casting; however, that could be only partially true.
And for the record, Survivor has brought back one contestant four times, until they finally won, and y'all do remember who that was.
Guangzhou hasn't been the location of tasks, but teams did have to fly there in order to reach Guilin in season 14. China is so vast with its numerous provinces and cultural differences throughout the country that it wouldn't be difficult to pick a previously unvisited locale.
I wouldn't mind India this season either, especially if Indonesia would be the alternative. And the first location does make Laos or Burma an option, and I would love to see one or both visited this season.