although Kelly has yet to actually post a full on "squat form" video noting stance width, grip, depth, etc, I have noticed most of the time he squats to demonstrate feet forward, he takes (not quite as wide) a more powerlifting stance width. I say this because a lot of people are worried about the knees being way outside the feet and creating sketchy unwanted forces, and this will certainly happen with a closer SS style width, but with a slightly wider stance the knees line up nicer with the feet (though the angles are NOT parallel).
So if you're truly experimenting with this, I suggest when you adjust toe angle, you also adjust stance width.
Personally, I've tried both for my warm-ups but have yet to try a toes forward stance for a heavy work set or max effort. Less to do with feeling unsafe, more to do not being as accustomed to feet forward. And I don't collapse my arches or cave my knees with toes out so I don't think Kelly's concerns apply to me.
That being said, I'm always open to trying new things, and figuring out what works best for the individual. I think Rip (hopefully) would agree that if you have a good base of strength and can perform a safe and efficient SS style squat but want to experiment with different styles that may lend themselves more to your anthropometry and enhance your performance, then by all means go for it. Otherwise stick to what works.