Ye, after-game content wouldn't quite work well; although, it's not a horrible idea to experience the rebuild. There is, however, more content in general being added to the game. Two guild quests, which Nico seemed very excited about implementing when he gets back in a couple months, called The Golden Sickle and Rha'lata(possibly). Also some crafting revisions to make above crafting viable after level 50. Other than that... I haven't seen anything else.
I do agree that the game should, like @Makesin suggested, have you appear in Ark after the credits end. Would be a nice addition.