There are many many countries who would be very interested in this bird if it lives up to its potential.
There are many JSF partners who are starting to look distinctly green around the gills at the F35's sky rocking price tag who might just be interested in the J21/31 (btw, wth are we supposed to call this birdy?), especially those keen to develop their own indigenous aviation industries.
So I can see Turkry being potentially very interested in this bird, especially if it comes with meaningful ToT. Egypt would be another prime candidate with the relationship already established via the K8 deal and the new Egyption president taking down the military and wanting to steer a more independent course from US influence, I think diversification of defence purchases would be of much interest to the new leadership.
In Latin America, I can see Brazil being another big potential customer as they are also keen to expand their own local aviation industry and the importance of Chinese trade to their economy and the fact that both often stand together internationally on key global decisions are solid foundations that China might be able to build on to expand into the military field.
In Africa, South Africa seems to be increasingly friendly with China, and so a big defense deal would not be all that shocking.
In the middle east, the J31 might find interested buyers in the form of the UEA because of the strong Pakistani connection, and also because I am sure the F35 they will get will be both more expensive and less capable than what Israel will get, and that will irk them to no end, there will also probably be all sorts of concerns about back doors, trackers and kill swithes in all the American black boxes that will be of serious concern to all export customers of the F35, so I can easily see them ditching the F35 if the J31 turns out to be a credible alternative.
Then there is always the 'old faithful' of Pakistan, who would almost be a sheo in as a lead export customer, maybe even at the expense of the J10B, which I am sure will secretly please SAC to no end.
The J31 would likely be really useful to the Russian air force and navy, but I think their pride would prevent them from buying any fighter jets from their old student and who their media continue to disparage and slander with copying accusations. However, many former USSR republics like the Ukraine and many a 'stan could be very interested.
In addition to purely commercial sales, the J31 would also give Beijing an interesting and powerful new political card to play against America. 'Hey Uncle Sam, here is the New Deal, if you sell any more weapons to Taiwan/stir up any more trouble in Tibet or with island disputes, we might just gift wrap some J31s to, oh I don't know, I mean where to start? Iran would love them for sure, maybe Syria too if Assad is still around, Chevez would love some too (again if he is still kicking by the time the J31 is available) and maybe Cuba would want a few as well'.