Entropia Universe it's quite possible and has in fact already happened. A group of players purchased a moon for $150,000 as part of the game's 10-year anniversary celebration. But it's not just a super-expensive piece of property, it's a chance for the owners to make something unique and long-term in the game world.
MindArk, the company behind Entropia Universe, offered the moon as a chance for players to shape something freely while sharing profits earned from the new location. That means that the investors have essentially licensed out a part of the game for their own development and customization even as it remains a part of the overall gameworld. The moon is expected to be fully added to the game in Q2 or Q3 of this year. If you're curious about the specifics in the community, you can check out the full rundown on the official site.