I agree in regards to the houses. In fact, I'm beginning to wonder if we're also misplacing Merida and Jack as a whole, mostly based on the fact that Slytherins, according to the Hat, are "cunning folk" who "use any means to achieve their ends." A Slytherin Jack would therefore have most likely taken Pitch up on his offer (perhaps even with the intent to double-cross him in the end?) in order to fulfill his ambition to be believed in and seen. Instead, he turned him down point-blank, turned his back on him, and started walking away (only to then surrender what he thought was his only means of power to save Baby Tooth - hardly a cunning move, but certainly a brave and chivalrous one). Meanwhile, Merida cunningly set up the suitor's contest so that she could crash it on a technicality of rules, win, and get what she wanted (which was out of the marriage thing), and that's not even mentioning buying a spell to force her mother to change. Sure, she learned to regret it in the end, but she didn't have any qualms initially.
A Slytherin who is courageous when it gets down to the wire and a Gryffindor with a deep personal desire. That's not really such an impossible thing, and I'm really considering drawing these guys in that arrangement.
Sorry for chatting your ear off! It's been on my mind for a while.