Just like a daily event, time limit, bad guys get stronger each wave. People will only do so much of this, kinda just add it to the grind I guess if that's what it's to be like. Weekly, nightfall and a few waves in the arena. I think I may start raiding again in the VoG, just to know that I will be able to upgrade certain items gets me more excited than this arena scenario at the moment. If this arena thing pans out then you will finally see true skill come out in the guardians across the world!