There's no realistic route for US aircraft at this time.
The PAF's only real next-gen options are either (1) go with the Chinese J-35 or J-21 or (2) work with the Turks on the TFX. The bare simplest option is the Chinese, but we won't learn a single thing and we'll be stuck (for yet another generation) relying on others. The Turks, on the other hand, are higher-risk and higher-cost (at least if we want to get serious workshare), but much higher reward (e.g., the potential for multi-billion-dollar aircraft production work in Pakistan, a heavyweight stealthy fighter, etc).
We should pick one of those two options for a 2030-2035 timeframe and, in parallel, work on our very own indigenous fighter for 2040-2045. For the latter, we should invest in feeder industries (e.g., gas turbines, IC manufacturing, composites, advanced steel, etc) that will propel our exports and help us fund our country and domestic defence programs. Those feeder industries will lay the groundwork for our own fighter.
I don't understand why Pakistan is slow regarding adding new technologies. We should be encouraging China to make J35 in partnership with us, if Pakistan also invests then am sure China will make the fighter faster than currently stalled project. J35 by 2035 is late because Usa/Europe will be adding 6th generation fighters. We need J35 by 2028 and then we can concentrate on 6th generation by 2045/2047. Adding 6th generation jet on our 100 years anniversary would be great, hopefully will be landing on the moon too.
Pakistan is blessed to have the Chinese and Turkish options, both great projects.