What I am about to suggest is not for my own sake, but rather for those new comers who are still trying to learn the game.
I propose a size limit for nations in the world. When a nation grows to 300,000 or 400,000 sectors ( 25% or 33% of the land, respectively), it should be kicked out of Sandbox (and maybe receive a message congratulating them on a victory in Sandbox).
I think it is clear how bad the experience would be for new users if they are being steam-rolled as soon as they start. (For an example, look at "sandzone", currently controlling almost around 40% of the world's land. At this rate, he could control the world before he is ousted. Hardly a good learning environment.)
What do you guys think?