4. An Age Of Ultron-Based Post-Credits Scene
The most recent Marvel cinematic universe release - Thor: The Dark World - had a post-credits scene related to the upcoming movie Guardians of the Galaxy. In terms of order of release, Guardians of the Galaxy will come two films after Thor: The Dark World. If that's anything to go by, Captain America: The Winter Soldier's post-credits scene will be related to Age of Ultron (which, for the record, comes two films after it). It makes sense because, in the trailer, Nick Fury talks of being prepared for things before they happen and that could involve S.H.I.E.L.D building a robot to fight for them (or contracting Tony Stark to do it for them) - that robot being Ultron, which subsequently goes rogue. It also makes sense due to the presence of Arnim Zola. As a weapons designer for HYDRA (or perhaps reformed and having worked for S.H.I.E.L.D), he could be responsible for Ultron's creation. The Winter Soldier himself looks to be something of a cyborg in this movie - that could be the first attempt at robotics that led to Ultron's creation. Either way, there are plenty of opportunities to include a sneak peak of Ultron in the post-credits scene.