Edgar Wright brought the idea of an Ant-Man movie to Marvel and it apparently had so much potential they decided to throw it into the new Marvel Movie Universe. It seems that early footage of the film has leaked on to the Internet, so hurry up and watch the video before the suits yank it down!
UPDATE: Less than an hour and Disney has taken it down. Sorry, but if you saw it, you now have an idea of what Edgar Wright is planning.
UPDATE 2: Vimeo has the video now, so you have yet another chance to watch the video.