And following with the rationale that they shouldn't date, it would also take away a main element of the show: Ally looking for someone to make her happy. I'd say that if she and John ended up together, it'd be for the 'long haul,' as in they're more meant to be than anyone else. That would be, like, an ending to the show, but not particularly a good way to sustain it. They need their friendship dynamic as part of the show....and that continuing sense of "what if?????".