If you really wanted to explore a flag for Earth, you'd engage people from around the world. What symbols are important to them? What colors? How do they want to be seen? What does it even mean to them to have a flag that represents Earth as something uniquely ours? And such. Then begin to distill these ideas down into a flag. Or try to create a process by which an idea could be brought about. And try to get buy-in from all of these diverse people. That's the hard part. The interesting part!
(Also, nitpick about the video: 5:8 != the Golden Ratio.)