Once PLAAF orders FC-31, some people will complain they are made to the needs of PLAAF, not our AF. Buyers will buy, window shoppers will not. FC-31 positions itself as being the only 5th gen jet available to countries who can't buy F-35. Possibly FC-31 has better technology than F-35 base model. If that is not enough, then you have to wait till 2040 or later until more options are available, if ever. So far, these promising projects all turn out to be paper planes in the end.
Now look, I am not trying to sell FC-31. Just saying the first customer will have a major say how the project will be developed. So if there is a need, I suggest interested buyers join the project sooner rather than later. If there is not a need, FC-31 will remain as a project in testing.