Player housing has shown up in a few MMOs here and there, but it's usually been more of a side project than a primary focus of the game. You placed homes, harvesters, etc. in Star Wars Galaxies, but for the most part those were more for storage and crafting materials. Ultima Online went a bit further with their housing system, giving players a variety of options for how to build their homes and what to do with them. This was still overall a side activity in UO though - you could work on it if you wanted, but the game was still primarily about killing monsters and your fellow players. If you've been looking for that game that was more about the homes and equipment you could craft that what dungeons you could raid, you might want to take a look at the Greed Monger project over at Kickstarter.