J10 is not necessary , The avionics found in j10A are same for jfthunder the difference is range and power. This explains that the upgrade package j10b can mostly be implemented on jft.
First of all there are certain advantages by design itself that the J10 offer, but more importantly is, will the Chinese be ready to offer JF 17 the upgraded AESA or avionics of J10? JF 17 block 1 didn't have the same KJ 10 radar as the J10A right?
So even if we expect AESA radar and IRST in JF 17 Block 3, it doesn't mean it has to be the same versions as in the J10. That means if PAF wants more capable fighters and techs, J10B could be a good choice above the JF 17, but if they believe that the difference isn't that much and that a JF 17 Block 3 could bridge the gap to the next decade till a 5th gen fighter might be available for PAF, J10B is wasted money.
China is not the US and will put less restictions on Pakistan and it's forces, but China isn't dumb either, they know how to make money and exporting J10 even more important to them, than exporting JF 17, which they see as an export fighter anyway. That's why they will keep an eye on how much Chinese parts there will be in JF 17 (radar, weapons, avionics and of course the engines in future), or of course on what technical limits it must have, to make J10B more interesting.
I said the same as Araz often before and think PAF should compromise and stick to JF 17 in higher numbers. Maybe not the most capable solution, but more suitable to PAFs finacial situation today and in the long run, which might free some more money to buy a 5th gen fighter later.
Pakistan as a whole could benefit from waiting even more than, procuring a foreign J10B today, since your defence industy could use available fund to develop an own AESA radar for example, that in future could not only be used in JF 17 B3, but in an upgraded version even in J31. That would not only increase commonality between JF 17 and J31, besides possibly the engines and weapons, but also would increase the indigenous content in both fighters.
JUST AS AN EXAMPLE, not as a discussion point!
LCA MK2 is meant to get an indigenous AESA radar and certain avionics, that later are aimed to be improved for AMCA. The Kaveri/Snecma engine (if developed) is aimed not only for AMCA, but also for LCA upgrades, so in both fighters can benefit from common techs at a point, which reduces costs and increases the indigenous content by far.