Few points
Thunder was desgined with modular design in mind.
GEN 3 PLANES needed continues upgrade because of the new technology so many blocks
In Regards to that what block 60 bought to F16 Thunder will get almost every thing in Block 3
Every air frame has its own limitation,
What are the future needs
2 main things
1 stealth figher which is expensive , industry cant support this project itself will need material and tech guidance from China
2nd twin engine more payload , flight time etc
You cant do both with thunder
Thunder can be upgraded but to a limit
For 2nd engine you need to actually redesign the whole airframe
So best option is upgrade 1 and 2 to 3
Build dedicated units for different roles e.g E.W & ground , sea based
Build numbers and leave rest for project azm build a plane which looks after future needs
Pakistan must try to have 300 planes as than you can phase out f7 , f16s , mirages
With a much better advance , version
While leave 100 to 150 for twin engine or stealth platforms
So Pakistan will maintain 400 to 450 gen4+ birds which shouls be enough for next 3 to 4 decades unless some thing changes dramatically