Oh my god, that would be an epic fic. Can you imagine him staring at shower curtains and things?! And then shaking his head because humans are so weird. (I managed to fight writing all that in capslock, go me)

And I totally second the whole 'it's going to ruin the show' thing. No it's freaking not. In fact, it's going to make the show delicious and angsty and wonderful. Am I the only one picturing Castiel flitting between the boys until he throws up his hands and tells them he's done with them? He'll be all 'I am not your mother!'