6. Alternate Realities / Timelines
Marvel ComicsIt's pretty clear that this movie, despite its name, will not have anything to do with the comic book arc of the same name. In the comic book arc, Ultron masterminded his assault on Earth from the safety of the future, using Vision as a conduit to do so - that won't happen here, but even a mere mention of an alternate timeline or universe would be a nice little nod to the story. Perhaps Ultron's departing words could involve saying "in this reality or the next", or part of his research - or the research of his henchmen - could be to look in to the possibility of time travel. So, without actually venturing in to alternative realities or time travel, just giving either concept a mention would be a nice way to acknowledge the existence of the comic book arc with the same name as the movie.