I usually avoid any kind of speculation like this because I prefer to just go with the flow and let the show take me where it will, but your post reminded me of a question I had after 5.13 and so I thought I'd ask your opinion. :o)

So here goes. Stupid question (and I haven't thought it through, so excuse the logic fail): But if the vessels for archangels (even temporary ones like John was for Michael) are in the same blood line, how does that explain why Nick can be a vessel for Lucifer?