Like I said before I think a dual engine like the FC-31 does not make sense for the PLAAF. Especially once the WS-15 engine becomes available. It would overlap with the J-20. I do not discount the idea of the PLANAF operating some version of it from land bases however. There are advantages to dual engine aircraft in terms of engine reliability. One of the reasons why the MiG-29 had two engines was precisely because of those reasons. At that time their engine industry could not ensure engine reliability at those performance levels. In an aircraft which is expected to conduct patrols close to the shore, over the sea, having more engine reliability certainly wouldn't hurt. This also might be the case in certain mountainous areas at high altitude. But as a J-10/J-7 replacement? Too expensive. See the experience of the Russians with the MiG-29 after the fall of the Soviet Union. The MiG-35 costs almost as much as a Su-30M with much less capabilities because both are dual engine aircraft. The WS-15 engine is supposed to have 160+ kN thrust and the RD-93 has like 80 kN thrust. Add to that the fact that the WS-15 will be common with the J-20 and that it will result in an aircraft with much less parts and it just does not make sense on mass production aircraft. Especially when the other side has the single engine F-35 in places like South Korea. With regards to the low production rate a naval only FC-31 would have. Over the next decade two more carriers, at least will become operational. That means four carriers. Add spare aircraft to replace broken ones, and aircraft for land-based trainers and the production numbers will be quite respectable. Especially if you use 3D printing the production costs won't be that high since you won't be using expensive die cast molds and things like that.