I love the dynamics between Fenris and Anders, especially during the second act, where they're barely tolerating each other, but you just know they really want to snap and snarl at each other. I always imagine that if Hawke were to romance Isabela this back-and-forth bitching between the two of them would evolve into something more, maybe the kind of convenience-sex Fenris has going with Isabela in canon, (only a lot more dysfunctional)
I'd love to see how Merrill would react to catching the two of them together, (and how they would react too) I can see her being totally confused "...but I thought you hated each other?" Even better if she was maybe the catalyst to them getting together in the first place because she's the only thing they can agree on.