Outdated thinking. Even if the engine cost double, the price spike would only be 5-10 million. Making it on par with J-10CE or even less. The main advantage is power and efficiency, the newer engines of China are now just entering what Roll Royce and GE had in the early 2000's. So the JF-17 could theocratically have more powerful avionics and allow room for Pakistan to develop better avionics for the jet, which could be more inefficient yet more powerful. Basically redesigning the outer frame slightly and adding new avionics. Also UCAV are not the main future of air combat, idk about Chinese but in arms-race Mao-dun is used about a weapon and it's counter measures, so basically UCAV might be flashy rn but soon enough a strong enough electronic countermeasure would come and basically make them ineffective. Much like how anti-air missiles made CAS completely redundant as a separate category. So no, the JF-17 has no parallels in the PLA as it is Grippen style take, infact the PLA has little to no experience in innovation in air hence why they're greenlighting all projects just cuz they have the funds. It's nothing new, infact the US did the same strats post-war allowing the technological creep that allowed US and West to dominate. So what Pakistan has for Block 4 is still speculation, however it's gonna be a larger airframe and redesign body. As you said, J-10 is a outdated design for the PLAAF, mainly due to it not having integrated EW or strong radar compared to the Flanker copies(as big radar in Pacific go brr), plus it's early role is completely redundant in the next decade. Compared to a new redesign JF-17, which could be enlarge and have a few structural changes to give it better rcs along with more effective EW integration room than the J-10. Props to Yang Wei ngl, he design this aircraft extremely good as apart from the size and a few changes because of requirements, the aircraft is a solid transitioning aircraft. Again assumptions, the choice of PAF is dependent on the requirements they have for the aircraft which could be different for each nation and their philosophy. PAF has a independent spirit for their air that is different compared to PLA or IAF, radar or range or electronics, everything is based on the requirements of the airforce. The J-10 is still a fantastic aircraft for many nation, while the Flanker is mediocre at best however due to Chinese land mass and other requirements they need to choose an effectively worse off aircraft. Tldr; don't make assumptions based upon your own nation's choices, China has dwindling pilot rollout hence they invest in unmanned craft, not because they're good but they can't risk a single pilot compared to PAF who has nearly 2.2 pilot for every craft making the craft more important than the pilot.