Sir,
In todays world it is all money.
F-16's are available as ADA for which no congress approval is required. Obama could do this by executive order. Unfortunately the F-16's that have PW engines are unavailable.
SU-35 have been refused by India because the SU-30 MKI are considered equivalent after the upgrade. Though this would take some time.
Russia knows the Indians would not upgrade these aircraft by using Russian technology but would ask Israel of France to upgrade them hence not getting enough case. So if PAF would like to purchase these aircraft then it has to have Russian equipment may be some western subsystems. PAF would still find it as a very viable option because it would open up the Chinese flankers as well as provide them with a new engine that could be used on J-10's and J-31's later on.
EFT would give PAF the same capabilities as the SU-35 gives how ever it would be somewhat difficult for Pakistan to get them to allow the EJ-200 engine be part of JF-17 or any other Chinese aircraft though the prospects of TFX and KFX open up exponentially.
Abb unth kis karwat baithta hai...