Imagine when at the end of the fate saga we stop the universe ending prophecy but can’t save earth and it is too far gone and dying. Humanity abandons earth to rebuild inside the traveler. As humanity finishes going into the traveler the rift the traveler heals itself as the earth explodes and the traveler leaves the Sol system behind out towards other systems. After traveling the stars for a long period of time imagine landing in a new system across the milky way or even in another galaxy all together. This is the premise for the next transition to a destiny 3 and could explain the retirement of our guardian of lore wants to start in a new character or try new light or we could continue with our guardian. It could even lore wise explain that due to extended time spend inside the traveler grows guardians closer to the light blurring the lines between classes. No more hunter or titan or warlock just light wielders able to use the light in any way they want. Eventually the traveler could be captured by an enemy faction like the vex or hive or new faction who would reopen the rift leading to our exit from the traveler again and finding ourselves in a new unfamiliar system with new planets and native species around.