I really like your definitions of the different kinds of AUs. You're right that those are all distinct and should have their own terms!

Your thoughts about the overlaps writers have to find are really interesting too. I came here after you commented on my response to this prompt where I said I'm not interested in crossovers & fusions, but now I'm mulling some over myself. I don't think I'll go anywhere with them, but it's interesting even just to think about :)