There are 101 reasons for sure, but there's fundamentally only 1 actual bottleneck preventing us from starting a real project: FCS. If we're unable to master FCS, we can't even do a proper system design and integration job using off-the-shelf solutions, much less design our own airframe. This is also the one thing PAC doesn't have a clear focus on due to various issues (attracting the right talent, for one).
That said, for everything else -- e.g., seeker technology, gas turbines, composites, etc -- we can start collaborating with other countries on 'high-level' R&D. Basically, we can't tie the R&D to a specific project like the NGFA, rather, we work with others on the tech for the tech's sake.
To the fauji-type, it'll sound like a huge red flag in terms of resource use, but this is actually the right way to do R&D. First, by keeping it abstract, you can pull in more willing partners (as there's no direct risk of military use). Second, we will build the capacity necessary to actually develop military tech indigenously. Third, we don't tie up scarce resources in solely defence, we can benefit economically from bottom-up IP generation.