99% chance is PAF wont buy Su 35.
Reasons-
1. PAF Docrine-
PAF doctrine operate single engine, meduim/ light weight fighter only.
Now J 6 was twin engined but was a lightweight fighter.
SU 35 is a heavy multirole fighter.
2. Cost- It will be very costly, judging that in recent MKI order, each MKI costed India 102 Million Dollars.
Even with discounts, the SU 35 will cost no less than 90 Million dollars (lifecycle cost+ weapons).
3. Its Flanker- Su 35 belongs to flanker familiy. There are similraities between both SU 35 and Su 30 MKI and after Super MKI upgrade the difference will be very less.
Plus IAF has operated flankers more than 10 years which means it knows weaknesses and stengths thoroughly, a fact PAF cant overlook.