Ability scores. Aside from the "extra bonus at even numbers" there's functionally little to no difference between an 18 (+4) Strength and just a flat out +4 Strength. Why not do away with the needless "18?"
Granted, the ability score bonuses you get at various levels would probably need to be reworked....
I think I'll just trust the designers and keep things as is.
But if I had to change things, I'd make magic items scale with players rather than the setup that so far looks like a continuation of 3E's magic system (but maybe not as needed).