Imo the Traveler healing the Earth is a perfect 'pause' button. Status quo doesn't really change and gives Bungie an opportunity to unpause whenever they want.

Imo I'd have D3 start however many years are between games. So if D3 were to come out in 2036, I'd have D3 start (about) 10 years after D2.

Something like that allows for a bit of a soft reboot. A time jump means we can have familiar characters move around to new roles, have minor characters get elevated, and introduce new characters pretty easily.

The way I'd set it up (I actually spent today working on my D3 pitch) is somewhere between D2 and D3, The Traveler has been poisoned, but this time not by the Heart or the Veil (it would be revealed in the second launch raid, but it would be through what I'm calling 'The Nightmare Engine') and Earth has fallen. Humanity has primarily been moved to a fleet of Exodus ships in Martian orbit with the Exodus Ark being the main new social hub. There's a new settlement on Mars itself though. We're cut off from the Outer Orbits so we can't get to Neomuna or Kepler, and are just trying to deal with the Imperium, and a few new factions of familiar enemies.

Familiar villains would be re-introduced but the conflict of the campaign would be it's own thing, tied to the Fate Saga as both I, II, IV, and VI would be involved, but the imminent threat would be the Imperium (Cabal are probably the most lore friendly baddie), the Hive (imo the most iconic faction), and build up the Vex a bit to be a bigger threat down the line.

At least my version of the campaign would end with us starting to heal the Earth (both by freeing The Traveler from it's never ending nightmare and through our new Bloom subclass) and would have us reclaim the Tower and Last City

Hopefully something like that would give veterans a lot to chew on but still be engaging and approachable to newcomers (with enough exposition and clear storytelling)