There is just one minor problem with the J-20. And that is the plane still doesn't have its intended engine the WS-15. If the J-20 should enter production in the next few years it will be with an uprated WS-10 or AL-31. The plane will be significantly underpowered. I suppose that the plane will pay for it in terms of maneuverability. Since the J-20 never flown on "full power" so to speak it never shown its full maneuvering capabilities if not speed and there for the plane is in part still untested. And when the WS-15 does become available the J-20 might need a new round of testing and perhabs some redesigning of its software if not airframe.
Whether they fly it with the AL-41F to WS-15, or jump to F-117S?, they will "open up the envelope" in flight test, here in the US, one or two aircraft would be reengined to do the "flight test" and the upgraded aircraft would be designated with a letter upgrade to B or C or whatever? The Eng has convinced me that Chendu has NO desire to go to OVT?? seeing it as costly, and of limited benefit to the aircraft/program, but they are interested in "super-cruise".
In my mind, the computer has taken the performance limits out to maximum projections, and flight test would only be "verifying" those results, hence not to complicated?? not likely to require any major redesign?? unless they ran into problems?