We already have mars as a playable location in D2. Bring back EP as an Arena playlist, no sweat, no hero/legendary/master difficulty just a fun activity in which people can play and get mainly open world loot and resources (cores, alloys) if they reach the final boss. Put giant Hive Guardians as the weekly bosses, and make free seasonal content around it. Escalation Protocol was not only the best public event in Destiny it was a great way for players to get resources and exotics.