It seems like there are a lot of people think WS-10 is a photocopy of AL-31F/FN, so it is easy to replace the AL-31s with WS-10s----just like changing the batteries of a digital camera----by the way of dislodging the old one and replacing it with a new one.
There are three photos I download from some Chinese websites.These photo were shot in some Chinese aviation exhibitions in Juhai or somewhere. The photos show WS-10 is entirely different with AL-31F/FN. Most Chinese sources call the plane with WS-10 as J-11B, that means there should be three variants of J-11:
1) J-11, China made Su-27 fuselage with Russia made AL-31F and Radar/avionics;
2) J-11A, China made Su-27 fuselage and Radar/avionics with Russia made AL-31F;
3) J-11B, China made mended Su-27 fuselage with WS-10 and Chinese Radar/avionics;
If WS-10 is not a duplicate of AL-31F/FN, that means it may have different characters like airflow, by-pass ratio and overall pressure ratio, even size, etc, so you can not simply put it into a Su-27 or J-10 fuselage and suppose the plane would work well. There are a lot of things you need to do. You need to change the rear fuselage to fit the size of the new engine, mend the air inlet and duct of the plane to match the air-flow of the new engine, and some test flly is also needed.
WS-10A passed its design-developing certification in 2005, obviously it was on J-11, that means all the works and changes for WS-10 on J-11 I mentioned had finished in 2005. It matchs the time that Chiina stopped import AL-31F engine from Russia.
About WS10 for J-10, I have mentioned AL-31FN is different to AL-31F, so if China decides to use WS-10 on J-10, they have to do the same works they had done on J-11---Changing air inlet, rear fuselage and makiing new test fly, all these need time.
On the other hand, AL-31FN is developed by Russian only for J-10, that means China must have promisesed Russian that they would purchase certain amount of AL-31FN(some Chinese source said it's 300) for no one would develope a turbofan for you if you only bought several of them. I suppose there will not be J-10s with WS-10s in PLAAF's fighter fleet until the 300 hundred AL-31FNs are used up. And then there will be a new variant named J-10B(like J-11B) or something with WS-10 turbofan.
WS-10A
AL-31F
AL-31FN