Let's assume the engines are the same -- what kind of motivation would CAC have to coat Al-31s with this new substance? Vanity, to make the plane look better?
Personally, I do not have an opinion as to whether the engines are Al-31 or a new type. We have eyeball evidence for both and against imo, and also the backing of maya for Al-31 while the likes of huitong is still calling the silver nozzles a WS-10 variant.
Btw, the argument you use for why it would be prudent to use Al-31 for J-20's "maiden flight" (if we believe the highly public maiden flight was indeed the first, which I think many of us doubt), can be reversed to ask whether CAC and PLAAF would allow the highly publicized (relatively) first flight of their pride and joy to be undergone using foreign engines?
Besides, by early 2011 WS-10s have been in service with J-11B regiments for a few years already so they're not exactly a brand new development.
Google T-50KNS. It is a T-50 prototype equipped fully but not meant to fly, using it instead for ground tests.
My line of thought is that is what the normal Al-31 equipped J-20 was relegated to after taxi flights.
---------- Post added at 08:45 AM ---------- Previous post was at 08:41 AM ----------
Round nozzles doesn't really have anything to do with what kind of flight tests a plane is performing, and the majority of the community believe WS-15 will be using round nozzles too.
Well we knew all along that we would see a J-20 prototype with WS-15's eventually, no reason to think specifically it will be WS-15 imo even with huzhigeng's backing (he's been wrong a few times now).