As far as the Arena goes Anet might think of some situation where the Arena gets heavily damaged by the AetherBlade pirates thus getting rid of the arena , and most probably building something else in it’s place , like a new and better improved training ground , that’s just my speculation I’m not really sure what they plan on doing with the whole thing once the Jubilee is over , but that idea seemed like the most plausible in my mind. After all the pirates broke into the arena once , what’s stopping them from going in again sabotaging the robots thus crippling the guards , causing a distraction , and doing their plan to damage / remove the arena at the same time. This is all just my opinion on the whole thing.