One for Sorrow

That line of Dumbledore's really seemed to confirm it for me. Because I don't think Snape really was a Gryffindor (I know some Snape fans think he really did change, but to me he seemed like a DE who also had a private love obsession that he chose over that), or that Dumbledore really believed that, but it was a compliment to suggest that in his later years he approached something like actual virtue. So he could die with the respect of Gryffindors and become like an honorary one. The important thing being that any way you look at it, Slytherins are constitutionally untrustworthy and inferior and will never get into heaven.