Personally I don't think there is any change in the wingspan of the J-8F, mainly because the program is already on a shoestring budget, Changing the wings and so on would cost valuable development money. The benefits of a longer wingspan wing would have been small, as I don't really see that big a difference to make it worthwhile.
It you really wanted to improve the wing design, it would have been to go with a double delta layout, which would have raised wing aspect and wing span for better low speed maneuverbility and angle of attack. Add variable camber slats on the front edge and so on.
But while all this would have improved agility, these will be offset by increased drag, and the plane would be slower. Since the plane was intended as a high speed interceptor and not as a dogfighter, this was a matter of setting priorities what you want the plane's mission role should be. As primitive as it looks, hard edged wings with wing fence is faster than wing with variable camber slats on the front edge. The F-86 actually with hard wings with fences on later variants when earlier variants used slats.
Increasing wingspan would not have helped the J-8F on high speed mission roles. The only perceivable aerodynamic difference would be adding another fence to the wing.
I also think J-8F, at least with later versions are powered by Kunlun engines, although this may have been progressive. The J-8F/H probably started first with WP-13B in 2001, then transitioned to the Kunlun, and later to the even more powerful Kunlun II. As WP-13s meet the end of their life expectancy and as spares run out, the newer planes in the PLAAF J-8II fleet maybe transitioning and upgrading to Kunlun engines.
