I am not a fighter plane expert. But having read a lot in PDF, I have some observation to make.
1. If the speed increases then it will be challenge for the pilot to with stand G-force and its mental condition and ability to handle the M/C. In Developed countries numbers of persons having both physical and good technical ability are less inclined to enrollment in to AF. And if there are casualty then it's putting the Govt. under pressure. So in my opinion the future development will be on Drones and ROBOT soldiers.
2. Now if the Drones are extensively used then the targets will be the command and control.
3. Now, can it be possible that country-2 which is being attacked can trace the signal issued to drones and find its location in country No-1 and destroy it?
4. Or can the drone system be hacked and bring it down or make the drone blind by LASER (by any means)?