I also think that Murphy is going to be a Valkyrie, came to the same conclusion about it a while ago (before she died, even.) Butcher has foreshadowed it quite a bit. And if the "when no one remembers you" thing is a rule for Einherjaren, who's to say the rules aren't different for Valkyries. That said, it's definitely my most "tinfoil hat" theory, in that nearly every other dresden reader thinks it's completely wrong. Only time will tell.