What are the predicted combat roles for the J-35, and how does it reconcile with the existing J-20? This question is specifically for the PLAAF J-35A and not the (expected) carrier-based PLAN J-35, since the J-20 (all variants) cannot be carrier-based.
The US F-35 was designed and currently serves as the multi-role 5th-gen fighter jet of the USAF. As they could not restart production of the F-22, leaving it as a limited and legacy resource that will inevitably attrit into nothingness, the F-35 (any variant) does not really overstep onto the F-22's role as an air superiority fighter in the long-term.
The situation is not the same for the J-35A and the J-20, since both are in production. There was speculation that the J-20 was a long-range striker or interceptor rather than air superiority fighter, but that was proved incorrect by the Chinese military itself which has classed it as a multi-role fighter. So what combat role does J-35A play? Having multiple same-generation multi-role fighters in production seems like an inefficient allocation of resources and priorities.
Or perhaps it does not have any difference in combat role, with the only reasons for its existence being non-combat related such as economical (cheaper units, "might as well" derivative project of original carrier-capable J-35 plan), industrial (experience for SAC, insulation if CAC becomes immobilised during conflict) and geopolitical (military export)?
As others have suggested in this thread, the main concern is probably cost and numbers. They want a order big enough such that economy of scale would also benefit naval version as there are currently only 3 carriers (imo only Fujian will actually get J-35s, seems like a hassle to make a cat and non-cat version).
It should also be substantially cheaper than J-20, with less range as the core drawback, which is not as much of a concern if it's main purpose is homeland defense as a land based fighter.
I think they will eventually settle on those 3 fighter types being the most numerous and complimenting each other in their roles in a Hi-Lo mix.
J-20 - top of the line, deep strike strategic assets
J-35 - cheaper, more numerous general air superiority
J-16 - missile truck, CAS, EW
As an aside, what was wrong with recycling the fc-31 designation and changing it to J-31?