It is 8 -10 years for paf to get producing 5th gen fighters
I do not know when such a plane would be designed, but the prospect sounds exciting. Given the practical approach of PAF, I hope it will be something real and actually in production unlike the "LCA" and whatever else India makes.
It seems that the design requirement is, possibly, IMHO, as follows (please note, I am speculating):
1. Stealth / LO features
2. Supercruise at 1.2 mach
3. Range equal to the F-16
The best way to design such a plane would perhaps be to keep it simple and work with available technologies. I am not an aeronautical engineer but I have informally studied it and I believe such a plane is possible within the parameters presented above.
Here is how one could go about designing such a plane - take design cues from what has already been researched rather than re-inventing the wheel (aka LCA / Arjunk / etc).
The closest aircraft to such a specification requirement are:
1. X-31 (delta wing, TVC)
2. J-10 (delta wing, potential TVC)
3. F-16 XL (Delta wing, TVC)
At the same time, one can perhaps look at the designs of stealth aircraft already produced:
1. J-20 (great design but less valuable for air superiority, a prime requirement for PAF and also too big and maintenance intensive. But could a smaller J-20 around a single engine be a broad possibility)
2. F-23. This aircraft lost the US fighter contest due to political reasons. You can see the only test pilot to have flown both the YF-23 and YF-22 basically hinting that the YF-23 lost because of politics and that it was a superior design. (can't post links yet but you can find on you tube "YF-23 Dem/Val presentation metz sandberg"
3. F-22. One interesting innovation in the F-22 is the use of TVC not to do cobra maneuvres but to improve high altitude performance. TVC can actually improve range, speed and stealth of an aircraft. See this paper for details how: (I can't post links yet due to not having enough posts but you can google and find the icas website paper ID ICA0534 a pdf file)
Taking these factors into consideration, perhaps the best design for a limited budget light-medium weight design is as follows:
1. A simple delta wing design. This provides the lowest drag and highest speed and range
2. A single engine like the WS-10 or twin RD-93s. Should give enough thrust without becoming an expensive and hard to maintain aircraft
3. TVC. TVC along with FBW (fly by wire) will allow a simple delta to be highly maneuverable, it will also allow the canted tails (below) to be very small, drastically reducing drag and eliminating canards.
4. Twin canted tails that are used for both horizontal and vertical stabilization, in a similar configuration to the YF-23 (but much smaller given modern TVC and FBW advances)
5. If a single AL-31 / WS-10 is used, one could ride off the upgrades and parts bin of the J-10.
These features should be able to achieve an aircraft capable of supercruise of mach 1.2, excellent maneuverability both at high and medium altitudes and an ideal strike and BVR platform able to meet any challenge India can bring.
Technically such a plane would be gen 5.5 given the reduced tail surfaces config.