It will only be seen by one person, likelihood is that they won't record it so we'll only get a second hand account, and since everyone will know when the cube is finally opened but nobody can fully prove they were the ones to open it expect thousands of hoaxes to spring up right after it happened, with stupid descriptions, or maybe even photoshopped screenshots or a animated video hoaxes from the more computer savvy bluffers.
Mass confusion. That is what will happen, and then after a week it'll probably be revealed in a youtube video by Molyneux for everyone to see, or more likely he'll sell the ending for $4.99 on the game site so you can experience it too to see how many people buy it as 'an experiment'.