During pre-production of any movie there is absolutely no shortage of creative ideas, story boards and animatics that end up unused; however, it is not uncommon for some of those unused ideas to show up later in films that are a part of a series. In that vein, it's quite possible that the inception of the MCU Ultron in Joss Whedon's coconut may have happened during pre-production of the Avengers.
In this animatic we see Tony Stark doing a little work while JARVIS seems to take on a little different personality, one very familiar to those of us who know the way Ultron looks at humans. Now, I'm not claiming JARVIS will evolve into Ultron but I think that this idea carried over into Shane Black's Iron Man 3 (Three-Disc Blu-ray 3D / Blu-ray / DVD + Digital Copy)