"Oversimplification of characters"; "Houses ill-defined"; "Ubiquitous and inescapable" -- this has a way-too-close similarity with gender, no matter whether the culture recognizes just the common two, or has a few more thrown in for good measure. So why not think of a house as one's Hogwarts gender?
OK, let me try a thought experiment. Suppose a Malfoy got sorted into Hufflepuff. Given that they, and their whole family, would expect them to be a Slytherin, does that make them a trans Hufflepuff? Are they at all likely to handle this well? And what about their relationship with their family if they embrace their Hufflepuffness?
And your thought about someone where there's debate about which house someone belongs to, that they "comfortably occup[y] a territory around [the line], unaware that people might even draw a line there", describes my gender identity perfectly. So thanks, I'm going to think of house identification as Hogwarts gender from now on. I bet it makes a whole lot more sense that way.
What your characterization reminds me of
OK, let me try a thought experiment. Suppose a Malfoy got sorted into Hufflepuff. Given that they, and their whole family, would expect them to be a Slytherin, does that make them a trans Hufflepuff? Are they at all likely to handle this well? And what about their relationship with their family if they embrace their Hufflepuffness?
And your thought about someone where there's debate about which house someone belongs to, that they "comfortably occup[y] a territory around [the line], unaware that people might even draw a line there", describes my gender identity perfectly. So thanks, I'm going to think of house identification as Hogwarts gender from now on. I bet it makes a whole lot more sense that way.
ETA: Oh yeah, "line in the sad" is a great typo!