I would assume (hope) that more writing would be done on non canonical couples, but that's probably why I rarely read QaF, because Brian/Justin just doesn't do it for me (Yay Ted/Emmett!).

As for QaF, there is some subtext there- Brian/Michael. Relative subtext (sure, they kiss all over the place) but it's there. And you can still write speculation stories (like Brian/Emmett, for example, though why anyone would do that is beyond me). Of course Brian/Justin is responsible for a lot of the fic, but then they don't exactly conform to the slash version of happily ever after. They're a pretty fucked up couple, so there is room to work with. It's just like an entire fandom of established relationship fics.