On the other hand, the development of any FC-31 derivative started almost a decade ago, so any further lead time for FC-31 variants should be quite truncated. One of the most time consuming parts in the R&D of a new plane is going to be aerodynamic testing and flight control system development, and from that standpoint FC-31 based designs should already be quite mature. Similarly, if any FC-31 derived design shares subsystems with the J-20, those subsystems should also be quite mature, which means all the systems integration testing should be a lot more straightforward, low risk, and ultimately pretty quick.What CAC did with J-20 was quite exceptional. I don't know if it's fair to expect SAC to proceed at the same speed when they have to develop 2 variants at the same time + completing development of J-15B.
Newer generations may not see the same staggered production schedule as older generations, since one of the primary drivers of the stagger we’ve seen historically has just been the rush to catch up and close the gap on fielded capabilities relative to other militaries. Realistically there will of course be a stagger I think. But it may not stretch to 2040. Furthermore from a resource planning perspective it might make sense for SAC to take over any stagger of fifth gen fighter production to let CAC focus on ramping up production for 6th gen fighter production, if CAC is indeed expected to be the primary provider of a 6th gen fighter.CAC has produced J-10s for 4 years after J-20 induction and GAIC is likely to produce it for a couple of more years. I think 2040 is more likely to be when they stop producing J-20s.
A lot of the quality improvements for the WS-10 likely spills over to other engine designs, because many of the WS-10’s problems were general to the quality of China’s engine production capabilities. Insofar as there are design specific concerns, the WS-10 was a higher risk design than the WS-13. The WS-13 was a copy of a known design, while the WS-10 was a bit of a kit bash development.engine could be something that slows down J-35 mass production, since WS-13 hasn't been tested as widely as WS-10s. I'm not sure how reliable it is right now.