On traits as a replacement: I wasn't imagining a simple 1::1 "bonus on strength stuff." Rather,the player wants their character to be a way -- a giant pile of muscle, a silver tongued con artist, a bookish know it all, whatever. Players often graft those kinds of descriptions on top of ability scores. Let's skip the middle man and just let the player write "Bookish know it all" on their sheet and be allowed to apply whatever the trait bonus is to things that apply?
So they get a pile of plusses that often do what ability scores and skills did - but broader than skills, and narrowed but less siloed than abilities?
13th Age didn't kill the ability scores, but does it have something for broad ranging skills?
For advancement, is there any danger of becoming a big heap of bonuses to remember like PF 1e (minus the ability obviously)? Or is it no different than what 5e has now?
Ability scores used to mean more (they gated a variety of class powers and spell casting). Without that it isn't totally crazy.
What else in 5e do you want to nuke. If much at all, at some point it stops being anything close to 5e, right?