4. On-Screen Clarification Of What Loki's Staff Is
During the first Avengers movie, it was generally believed that the staff wielded by Loki was powered by the Tesseract. HYDRA's similar weapons were powered by it in its previous appearance in Captain America: The First Avengers, after all. As it turns out - as confirmed by Marvel president Kevin Feige in a recent interview - that it actually contains its own Infinity Stone, believed to be the Mind Stone. Unless you follow the goings on with Marvel Studios and its people away from watching the movies themselves, you won't actually know this, so Avengers: Age Of Ultron - which is set to feature the staff quite prominently - needs to explain exactly what it is. The mid-credits scene of Captain America: The Winter Soldier certainly opened that door. Baron von Strucker was revealed to be in possession of the staff (which will probably end up in the Avengers' hands after that) and he explicitly stated that there was more to it than anyone previously knew. Hopefully this means the "more to it" will be heavily elaborated on in Age Of Ultron.