I don't think they would do it again anytime soon. You have to be able to sell your setting to players, and we're such a divided fanbase (and world) that anything you do is going to be offensive to someone. They have established IP - they're better off running with it.
If they held the contest anyway, I'd submit a setting that did what Eberron did right:
1.) It is an analogy for a real world time period.
2.) It is designed to run with campaigns starting at a set moment in time rather than redesigned constantly to advance the timeline.
3.) There would be a lot of story hooks and no specific plan provided to resolve the hooks - allowing a DM to develop them (although many of them would have subtle suggestions on how to resolve them).
I'd use a world heavily inspired by Earth in the 1940s. Within this earth, the use of the first nuclear weapon would have broken the seals that contained magic. As a result, the world, which had been tied off from all magic for 1000 years, would have suddenly had access to magic.
We'd see ancient magical civilizations that had shifted off earth once upon a time return (Atlantis, etc...), we'd see holy wars erupt as long abandoned Gods return and seek followers in a world with organized religions, we'd see relics of old suddenly start glowing and revealing that they had power. The great war would be over, but the world would still be at war in small skirmishes. There would be no place in the world void of conflict raised by the return of magic.
The campaign would be set 2 to 5 years after the breaking of the seals. The arrival of magic would have had some immediate impacts (a new continnet appears in the oceans), followed by a slow build towards more extraplanar intrusions (more and more creatures traveling by portal or extraplanar ships to this 'real world).
Corporations would be hiring anarcheologists to find and explore places across the globe where magic might have been long buried. The PCs would likely need to work for such an organization in order to be licensed to use magic - if they want to use magic. Most weak magic items would not have survived the 1000 years without magic to hold them together, so we'd mostly see newly created magic, magic taken from off world, or great and powerful magics that the years and sealing could not destroy.
We'd have fledgling magical universities that struggle to master magic. These would be dangerous places filled with people pushing limits, reliance upon extraplanar trainers that might not be the best allies, and other perils. We'd see 1940s technology mix with fantasy magic - sometimes seemlessly, but sometimes causing unexpected impacts (such as using powerful magic tending to cause explosive materials to ignite).
In the backgroud would be the setting blocks for a storyline that reveals it was not the nuclear explosion that broke the seals, but a more more ancient force ... one that perhaps was not sealed away like everyone thought and has been guiding the world for a millenia towards a goal that is unclear at first.