When the #CoulsonLives movement began the moment The Avengers opened in theaters to break box office records across the world, one of the most common theories from Marvel Comics fans was that Coulson could return as Vision - the android Avenger who has ties to Scarlet Witch and is created by... you guessed it, Ultron - the villain of The Avengers sequel (Age of Ultron).
In some way, The Avengers will have to face the reality of Coulson still being alive - and there are now several characters who could have history with Coulson in the films and who do have history with Vision in the books.
Clark Gregg tells E!:
"I was a big fan of the Vision theory, although I wasn't sure I wanted to be an A.I."
Verdict: If Vision is to be introduced, it would likely be after meeting Scarlet Witch and Ultron.