[quote=@Crow]
Loosely, huh? So, do we [i]make[/i] worlds for this or are the worlds used here based on existing worlds in involved franchises?
[/quote]

A little of both. I have set 'destination worlds' in mind that I'm keeping hidden, but I may also take from character timelines I like. 

The main theme here is alternate timelines, that is alt history. But worlds from existing franchises rooted in or explained via alternate timelines are acceptable too (something ala Fallout or Halo, or etc). Given that it's basically literally the split of time into alternate universes, the sky's the limit essentially from where you can have your characters from.