I think this is a good possibility. By "a Carl" I mean a kid who has basically lost their sence of morality, making them cold, and more calculated. And I don't mean like Becca. Becca is a bitch, but Carl kills in cold blood for barely anything. (like the fleeing kid in season 3 of the tv show.)
It would be interesting if there was a character like this, close to Clem's age, as I could picture the obvious tension between them and Clem. The character could act as a sort of semi-antagonist, pushing Clem to lose her morality by making certain choices. I can't have been the only one who's thought of this scenario.