I have been reading different editorials and various blogs and I wonder how come everyone is so sure about Tony Stark being creator of Ultron. There are official articles that state that Captain America: The First Avenger will directly lead into Age of Ultron, so if Stark was the person to create Ultron then there was supposed to be some hint in random that he is planning to create Ultron but no, all he had was a semi AI Suit that was so dumb that it cannot evolve to Ultron in 100 years even if it wanted to.
I believe that first Avengers movie itself dropped hints about Ultron. Remember when Captain America and Stark find out that SHIELD is working on weapons of mass destruction that itself feels like SHIELD is working on Ultron project with or without Pym's involvement( If he haven't showed up on screen that doesnt mean that he is not present in MCU)
There is an article floating aboutt Avengers animatics and one of them hint to an evil JARVIS. So how does JARVIS becomes flawed? Did someone rigged it, or planted a virus?
The answer is yes and we all know who did that to bypass Stark's security codes.
You might bash me for bringing this theory again but with Coulson coming back on Agents of SHIELD this is the biggest possibility that while Coulson who is actually an LMD, while trying to rig JARVIS to access Stark's security accidentally or intentionally planted a virus.
Also according to a news few hours back it said that "Ant man is going to be a redemptive storyline" so if Hank Pym has no debuted in MCU then what is the redemption for? I guess he had a role in manipulating Coulson or some dark past with SHIELD that leads to Ultron's attack he just doesn't know that it happened because of him.
Other than I wont go into depth talking if Coulson becomes a villain (may be Ultron himself) by the time Agents of SHIELD ends on note of him realizing that he was LMD all this time and feels betrayed. But I believe that something like that is likely going to happen.