You are absolutely right in observing that the J-31 is not as yet ready. The development is continuing, and unlike the Indians who have declared the LCA Tejas operational for propaganda purposes, the Chinese will only put it into production once it has developed into an integrated weapons system. However, I don't think the J-20 has matured either and in any case, it is highly probable that the J-20 will not be coming to Pakistan. Reasons can include the Chinese avoiding to export it to keep its technology safe from the Americans, and it being too large for Pakistan's requirements. I say that because we have also seen how the PAF has avoided inducting twin engined planes up till now and the J-20 is a massive plane which most definitely will judged as overkill for the PAF. The J-20, and the J-31, also lack suitable engines. Both of them are powered by older Russian engines which are not up to the mark in competing with the engines installed in the Western 5th Generation Jets.
So it seems like the PAF will focus on developing and commissioning a potent force of JF-17s. With integration of SD-10s and AESA, the JF-17s are as lethal as the SU-30 at those ranges, since they will be deploying the same weapons as their opponents and will be operating on home turf under their own AWACS coverage. The JF-17s will also help them streamline MRO support and training programs. With the money that they save, they can then look at the latest planes available at that time. In the meanwhile, our F-16s will provide ample deterrence for any misadventure by the IAF. We must remember that any aggressive force must have a numerical superiority of 2.2:1 to have any chance of a successful strike, and the IAF cannot muster that for another 10 years at the current rate of modernization of both forces.