I'm thankful this type of problem hasn't come by my desk so far, but at this stage in the game I would assume that there would be a number of mature libraries for doing the ie8 iframe shuffle. I wonder why they went with a custom solution.
After going down a rat hole of implementing a cross browser file input recently, with transparent overlays and special iframes and all that jazz... definitely will be looking to use filepicker in my next project that needs it.