what would you even expect to happen on an ability crit?

Extra information, owed a favour, make a friend, get a small reward, get a clue to a larger reward, impress someone important, uncover a secret, get forewarning of a danger, hinder a rival, gain advantage on something, opponent is exhausted/confused/embarrassed and must pass a saving throw to act...

Skill check crits would be just like combat crits except there's way more scope for fictional as well as mechanical benefits.