Avengers: Infinity War - Every Character Confirmed So Far

Confirmed By: The plot. Vision has an Infinity Stone in the middle of his forehead and won't be appearing in any of the other Phase 3 movies in the run up to Infinity War (barring a cameo), making it unlikely anything will happen to stop him appearing.

Also, the Russos have openly discussed the fact that they want to explore Vision and Scarlet Witch's relationship in the movie, which would be pretty difficult if he didn't turn up.

Plot Predictions: Having accidentally almost killed Rhodey at the end of Civil War because he was "distracted by love", Vision's burning robo-desire to robo-seduce Scarlet Witch will no doubt play a big part in the background of Infinity War.

Probably just enough to make us all care enough when his head is ripped off and Thanos steals his life-force for jewelry, in fact.