As we all know, Quicksilver and Scarlet Witch are being used for Avengers: Age of Ultron.
There's been a lot of debate as to whether they should have been included in the film. Many believe that Ant-Man and Wasp should be used in favour, because they would serve more purpose to the story. Personally I think from a narrative perspective it makes more sense for the audience to emote with Tony Stark over his creation of Ultron than Hank Pym who wouldn't have been built up prior to the film.
Most of the debate has been about Marvel trying to "mark their territory" with Quicksilver and Scarlet Witch, especially Quicksilver.
A lot of people seem to forget Scarlet Witch's connection to Ultron's "son"
The Vision. I think it's quite likely we'll see Vision in the film. I can't imagine more than one Avengers film being based around Ultron, so this would be the best time to introduce him.
I would imagine he would serve as an antagonist throughout the film, working as a pawn for Ultron. Well, until the climax of the film when he ultimately betrays Ultron helping the Avengers take him down. Scarlet Witch could be the catalyst that humanizes the Vision during the course of the film.
Sound your thoughts out in the comments.