If and CAC develops their medium weight 5th gen, things will get really interesting.
I would expect CAC's medium weight to be single engined so that it would share the same powerplant as the J20 for logistical savings as well as because of CAC's experience with single engined types like the J10 and JF17.
I can see the PLAN preferring the twin engined approach for added safety, while the air force might prefer the logistics savings from having a common engine.
That is, of course assuming that CAC does come up with a medium weight 5th gen. CAC is very capable, but just looking at the sheer number of projects they have running, and it might be a case of project overload for them.
In addition, I have long held reservations about whether it is necessary or even wise at all for the PLAAF to follow the American model and go all fifth gen.
I think it would be much better for the PLAAF to just have the J20 as it's only fifth gen fighter, and buy them in decent number as opposed to what happened to the poor F22.
For the strike role, I think a J20 sub-variant with twin seats, larger and deeper weapons bays for heavy ground attack munitions like what the FB22 was to the F22 would be perfect.
For the PLAAF's future lo-end fighter, a J10C with WS15 engines and redesigned fuselage should be a step up from the likes of the Typhoon and Rafale and be more than enough to meet the PLAAF's needs.
This SAC design would serve as the PLANAF's future carrier fighter to serve alongside the J15, and also act as China's export fifth gen while the J20 is kept strictly off limits.
If this is how it works out, it would be quite amusing actually. Because I think it is almost a certainty that this SAC 5th gen will use the WS13 engine as it's powerplant, thus the arch rivals at SAC and CAC would actually present a high-lo mix of the J21 and JF17 that would actually work extremely well as a pair.