To clarify, it's not a rumoured backstory, just a non-canon ship :) I used to be a huge Severus/Hermione shipper. Why? Because I found the whole teacher/student relationship hot. Of course after Hermione reached a certain age :P Not to mention they are both smart, powerful and they seem a better match then Ron and Hermione have ever been.
I'm still quite fond of the pairing, but I moved onto slash lately :D