In the clip, Robert Downey Jr. is referring to the plot of the second Avengers flick Age of Ultron, in which Tony and Bruce secretly work on a global defense program called “Ultron” using the artificial intelligence in the scepter containing the Mind Stone.
The “Ultron” project of course goes terribly wrong when it becomes the main villain of the film.
Hmm… makes you think that maybe there’s a larger plan at play here, doesn’t it?