I don't see how that will let you deliver root/su in anyway. That simply lets someone modify an APK without breaking their signature. In other word you download AngryBirds from some third part, it looks like angry birds, has Rovio's signature, BUT has added/modified code to grab your files and data or trash them. I don't believe this uncovers any root exploit that would give any app code the ability to remount or modify the system files.
Maybe I'm wrong(hope so), would love to have real root.