A lot depends on how much you can fit a nozzle designed for one engine onto a different engine design.To me the use of WS-10 TVC style nozzles make perfect sense. It has already flown with a test demonstrator for several years and since it is unlikely that they’ll integrate it with the J-10s, all that acquired knowledge would go to waste if they don’t integrate it with the J-20. Going for F-22 style TVC nozzles seems like reinventing the wheel when China has neither the time nor funding to play around with new designs.