I say no to Valkyries.
Valkyries basically escort dead heroes to Valhalla, where they train and drink and fuck until Ragnarok. Valkyries are basically Viking receptionists. In fact, the name Valkyrie means "chooser of the slain".
I don't see the point in Valkyries. Your interpretation of Valkyries is also very undesirable. Even if we change your "Valkyries" to something else, it's still pretty specific. Your idea, sans Valkyries, reminds me of one of Toady's plans for artifacts. Maybe, there's an artifact that when you use, there's a chance of some non-Valkyrie entity appearing to help you. Let's say this non-Valkyrie-appearance event happens like, once every hundred, and the rest of the time Urist dies. That could be plausible, Valkyrie or no Valkyrie. Your Valkyrie elixir idea could be like that, but that's already a planned feature. Talking about Valkyries in that capacity is therefore a useless endeavor, since Toady's already got that on his mind. Beyond that, I say no to Valkyries.
I hope you notice that all my sentences have "Valkyrie" in them. I hope you're sick of the word "Valkyrie" and you will never use them again. Valkyrie Valkyrie Valkyrie.