I think "end game" is a thing of the past. Unless you're playing a game with a beginning and a set end, there isn't an end game. This game is always undergoing changes and more content is being added. Even if the devs were to finish A17 and say "That's it, finished product." there still wouldn't be an end game. Survival games, and MMO(RPG's) don't have an end game. There's always something to do, unless you've done it already. If an end game could exist with 7 days, I imagine it would be playing on the hardest mode, max zombies, toughest gathering settings and the harshest penalties for dying (like drop everything on death) and still be good enough to thrive.