We already know what it takes to make good (fighter) pilots: cognitive ability, emotional stability, and motivation to succeed (https://diginole.lib.fsu.edu/islandora/object/fsu:180418/datastream/PDF/view). But leave it to the USAF to never read the studies they commission from RAND.
When I first started in the flying world, I personally over-emphasized being technically smart - after having done it for almost 20 years, I'm convinced physical/athletic talent is an important component as well. Not to the point of being a division one athlete, but you should be above-average smart with the general ability to play most sports.
As far as the PPL influencing the PCSM goes, I do think it matters since it's both a proxy to measure how motivated someone is, as well as a measurement of their ability to fly - there is at least some correlation between someone having a higher propensity to succeed in UPT who has a PPL vs someone chosen randomly from the population. I know the AF knows this, but the current effort is motivated by a desire to "uncuff" themselves from perceived restrictive selection criteria so they can implement whatever X-action program they want in order to have the right shade of skin flying their airplanes - not because current selection programs aren't actually working. Seems like fraud, waste, and abuse to me, but what the hell do I know?
Besides the above, I'm already certain it won't work for one simple reason: the balance of male/female cadets at USAFA (~7:1 while I was there) is not mirrored in the fighter pilot community (or the pilot community at large). These people are of equal talents, with equal access to UPT, with equal ability to fly, yet the balance becomes lopsided immediately after graduation. There are other factors at work that "select" for pilots - PPL at USAFA didn't make a difference, and it won't make a difference elsewhere.
Personally, I believe that great nations will inherently be diverse - talent has no color or sex - great nations know this. I don't think that logic works in reverse, though I suppose we'll see.