The problem with a lot of those suggestions is that they don't form a uniform progression system. Which is fine for a point based system, but wouldn't work for d20. If you want to do d20, you need to have classes.
That's easy enough actually, look at the JLA. There are archetypal heroes.
Fast hero: Flash (all three of them), Impulse, Johnnie Quick, Jesse Quick, Max Mercury, QUicksilver, et al
Strong Hero: Superman (he fits into a few, super multi-class guy), Steel, Captain Marvel, the Thing, The Hulk, Wonder Woman
Ultimate Human: Batman, Robin, Huntress, Batgirl, Nightwing, Green Arrow, Captain America
Artifact enhanced: Green Lantern, Wonder Woman, Starman, Blue Beetle, et al.
Alien: Skrulls, Superman (again) Martian Manhunter, Hawkman, a million others
Under-water lord (AKA, stupid heroes): Aquaman, Namor, Aqualad, Fathom
See, those are your classes. Superman has about 50 levels and cross classed into at least three (Strong, alien, and energy projection). Flight is a feat, I'd assume, though it has various levels, so maybe "flying" is a class.
So there's a challenge. Do you make "flight" a class? What if flight is given because of a doohickey? Obviously, the system needs some arrangement. And you've got races. I think it could be overcome though.
and btw, CURSE YOU FELL FOR FINDING A WAY TO DO THIS THAT INTERESTS ME!
Now I have another frickin' project on my plate.