A cool little site I started following recently, Unleash the Fanboy (UTF) just put out an exclusive that, if true, will absolutely tie some things together from Iron Man 3 and Avengers: Age of Ultron. According to UTF, Paul Bettany (the voice of J.A.R.V.I.S.) will also voice Ultron.
UTF claims to have a source, inside Disney, that shared the info with them and when asked if J.A.R.V.I.S. or some other form of Stark's AI programs would ultimately become Ultron the source replied, "That's the plan so far from what I've heard. Obvious, isn't it?" And, to answer the question, yes! Marvel and Joss Whedon are very comfortable moving away from the comic book origins and stories to focus on what will work on screen with the characters they have established. We have known for some time now the Hank Pym won't be Ultron's creator as he was in the comics so Stark becomes the next, logical step.
Given where we saw Stark's AI go in Iron Man 3, in addition to the unused Avengers concepts of J.A.R.V.I.S. seemingly showing some evil-tude (which I speculated on the other day as the genesis of Whedon's ideas about Ultron as the villain) this really does seem like the most logical path to Ultron. EDIT: it was just pointed out to me that the SDCC footage did show Ultron morph out of Iron Man's helmet. Seen through a new lens given the current information, that teaser may have been much more telling than anyone really knew. Silly Whedon.
So, Bettany will, apparently, be voicing Ultron going forward and that's an idea I like quite a bit. I've always loved Bettany's take on it and the fact that he never knows what the movies are about. He's explained in the past he usually just comes in at the end to do some voice work and is clueless about the plot, etc. I'm absolutely going to be going back and rewatching the Iron Man films and the Avengers through with the focus on the evolution of J.A.R.V.I.S. during those films.
Clearly not confirmed, but a sensible rumor unlike some that have been flying around the past few days (AquaDamon, hrmph, hrmph.) I'll keep you in the loop!