I actually share the idea that a perfect game is the one that doesn't require content updates from developers to keep being interesting. To that end I came up with a few thoughts on the matter. A game becomes boring after awhile if it doesn't have new content. If developers aren't the ones adding the content, then players should be the ones to do it. The player's motivation however is radically different from the developer's. The player wants to enjoy the time spent with a game, developer wants players to play the game and earn money from that. So either the players have to become developers themselves or the game has to offer the kind of gameplay that allows the players to enjoy creating content in the same way they enjoy playing a game. The first approach is the one chosen by the creators of Second Life. The second approach is the one chosen by the creator of Minecraft. However neither of these products are actual games where people enjoy playing together in a PvE fashion. Surely there are times where you would enjoy fending off zombies with your peers but that kind of gameplay gets old fast. What's more interesting is competing with your peers, and that is the essence of PvP.
So to recap, you need:
1. Content generated by players
2. PvP
Unless of course you can somehow make a system that would generate new content on its own in an evolutionary fashion, adding new locations on the map, new monsters and everything else, without the designers doing so much as lifting a finger. I don't think that's possible yet though. Maybe in 50 years time.
I actually already came to those conclusions already in OP and a second post in this thread.
Content created by players = Terraforming, building houses (towns, communities). And MODs for their own servers.
Sadly none of those options would fit into my game..