Originally Posted by Dr. Evil
The news about Spader as Ultron still means that the Avengers will probably face an army of Ultrons. Jocasta is unlikely and the Vision is a long shot, although not impossible.
Jocasta (in all her comic iterations IMO) is too goofy to be included in the movie. However, I would put Vision in the "just south of likely" neighbourhood.
If I were to make random unsubstantiated guesses, Ultron could take over, "upgrade" and build JARVIS a humanoid body as an F-you to Tony. I'm thinking Ultron, perverse sensibilities and all, would be delighted by the thought of Stark's (arguably) greatest creation destroying Stark and possibly the rest of the Avengers. A sentient JARVIS/Vision then overcomes Ultron's programming and... well, we all know the rest of that particular drill.