7. Loki's Return
Idris Elba let the cat out of the bag when he confirmed that both he and Tom Hiddleston will return as Heimdall and Loki respectively in Avengers: Age of Ultron, but based on how Thor: The Dark World ended, it seems likely that Loki's return will be more of an Easter Egg than a starring role. However, unless Anthony Hopkins is also going to appear (as Loki in disguise as Odin), the God of Mischief will have to be up to something fairly significant here. Could it be that Heimdall sees through his tricks and is murdered by Loki, setting up the events of Thor: Ragnarok? That's one of any number of possibilities - another is that Thanos will attack Asgard in search of the Infinity Gauntlet and Tesseract - but don't be surprised if Loki's "return" is used to tease something even bigger for the near future. After all, the Mad Titan likely still wants revenge for how Thor's brother failed him in The Avengers...