No DLC after Taken King has been announced so far. No Season Pass, nothing.
So we do not know how additonal content will be provided so far.
Endgame is endgame, like with any MMO it will consist of you finishing up content you haven't seen yet or not doing content you do not find entertaining) and you basically set your own goal. Whether you grind till you have everything or just play casually with friends and such or even stop playing till new content you care about comes out, that's on you,not the game. Endgame is up to the player,always.
PvP design is "shoot men with guns". Will they change balancing? Sure, but that's it. The PvP is supposed to be a fun side activity, that's how Bungie has been labeling it.