@Nocturnal_Stillness, Yes I like that. The story could include 3 or 4 (probably no more than 4) totally different worlds and sets of characters that way.
And of course if only 2 authors decided to collaborate, you could just do the tried and true “x versus y!” (with matching title) although x and y would really only fight for about 5 minutes of reading time and then they would of course team up.
I just found it funny.