Destiny is a 10 year journey. So since there is a possibility we may get to keep our character throughout (nothing confirmed) I was thinking...
What if our character aged over the years, like actually grew with us?
EDIT
This doesnt mean you'll be old and and useless, we're talking your character aging from 20 -> 30 years old.
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You know what would be the best thing ever? Scars. If not only you got more wrinkled or your skin got aged by the years of battle, but if you could get scars, that would be amazing. It would be very complicated to determine when or where in which battles you would get one, but maybe it could be up to us. I don't know, but scars would be like the prove and memoires of many battles and fights, and it would be awesome :D