China's 5th generation efforts are many years away from reaching the international market, there is very little point in discussing it in the context of today's PAF. I think given the nature of Chinese-Pakistani defence relations, we can be assured that the PAF will keep abreast of the J-31 program, they're not oblivious to it.
As MastanKhan said above, the PAF's priorities at this time are focused on JF-17 and acquiring additional medium weight multi-role fighters (ideally F-16C/D). Besides this, PAF is apparently looking for a twin engine fighter for use in Southern Command's maritime theatre.