Throughout Harry’s time at Hogwarts (and the Mauraders, and the Weaslys, and Voldemorts, etc etc) the Sorting Hat looks into the hearts and minds of new Hogwarts students and decides whether their personalities suit them to Gryffindor, Slytherin, Ravenclaw or Hufflepuff Houses. It’s canon (per the Sorting Hat’s various songs) that when the school was first opened, the Founders chose their students personally, and the Hat was only brought into play when it was clear that the school would outlive the Founders themselves.
Besides the obvious questions of how they enchanted the Hat and how it chooses the Houses for the students (is it evil, since it thinks for itself but you can’t see where it keeps it’s brain?), I’m curious about how the Sorting went prior to the Hat coming into play.
How did the Founders know what the student’s most prominent personality traits were – did they put the students through a series of tests, or were the students just required to come with several letters of recommendation from people who knew them at home? Did the Founders ever fight over a student? I can see them fighting over someone like Harry, who was famous and would bring prestige to the House just by being there, or by Hermione, who was clearly split between Ravenclaw and Gryffindor traits. And if they did fight, how was it handled? Did they duel over students? Or – more boringly – ask the student him- or her-self what house they wanted to be in (that’s probably the most likely solution, considering the Hat Sorted Harry into Gryffindor over Slytherin at his request).
These are the sort of questions I wholeheartedly believe JK never believed anyone would ask while she was writing these books.