Great idea but I wouldn't bother. With the retconning you could see chunks of your project get removed from the lore. My advice is just to compile and bullet point the existing lore. See what D2 lore, compile that and wait till we get some news about the direction about where they are going with the Darkness and other stuff. Then you start and at that point you'll have it laid out neatly already. Considering the importance of the Darkness and how it plays into the lore, I'd hold off. It sucks, Is like to see a nice lore guide, but I don't want you wasting time getting deep into stuff that might not stay canon.