Here's Mine:
Jason Bergman hinted some time ago that Fallout 4 might take place around the Mojave. We know now that isn't true, but it's an interesting thing to say given that the location for Fallout 4 was almost certainly set by that time, and Boston has zero relation to the Mojave desert. Considering Fallout 4 seems to occur chronologically before New Vegas, I'd like to see what the Divide looked like before it was destroyed. Naturally, there's a good chance this will be one of those "go there once and never return" DLCs that we got with both F3 and New Vegas, given that the Divide is invariably blown to bits by a certain Courier. Maybe we'll even see a bright and cheery Ulysses before he went emo.