So I always had this idea that at some point, a student was found to be an equal/nearly equal mixture of 2 or more houses. Like ravenclaw/slytherin. So they were put into a new house - Ravenrin or something. And Ravenrin would be different from, say, Slytherclaw. And in the end there was a house for special people that were equally displaying all qualities. Slytherclaw-Gryffinpuff or something. And in the end Hogwarts ended up growing a lot bigger. Does that make sense?