In all honesty, the player characters in destiny are just empty shells - they don't really speak, they don't make choices, there is no right and wrong. We may like the way they look and like their equipment, but as any new expansion (or whole new game) comes out, we change the way they look and the weapons and armour of choice. That being the case, I think Bungie could achieve both aims - letting us take our basic character models forward but also effectively starting again from scratch in a new game. I am thinking of some kind of surprise attack on the tower and the traveller, which forces the guardians to leave. The attack destroys the equipment vaults and drains or blocks the traveller's light - as a result when the fleeing guardians land on whichever new planet, they have no equipment, their light is dimmed (which could reset subclasses if Bungie wanted to), and effectively they start again. All that would require is for the basic character model to be carried forward to the next game.