I've been thinking about this, and here's ideally how the cube would have opened:
- The winner would have won, and decided to watch the video before sharing it.
- After watching, he would decide to not share it, keeping 'God's' identity, and existence, secret.
- Molyneux would relate this, with vague statements like "I did win. Believe in me, and believe I do exist", which alludes towards God.
- Everyone would be disappointed.
- As Godus releases, God's influence would eventually become apparent. At this point, Molyneux could start revealing the information.
- People could reflect on how it was clearly life changing, for this God.
It is inherently cooler as a secret. What's inside of the cube is amazing, because the very knowledge of what it is changes the worth of it.