So this idea is you can take your guardian and play the story mode again from the very beginning on a higher difficulty with higher rewards. To be able to do this the character the player is using must have already completed the original story missions and be atleast lvl 32. The mission difficulty would be increased but the rewards would also increase. Also you would be able to see your character with his/her amazing new weapons and armor in all the cutscenes (that you can't currently see them in because some cutscenes can't be viewed more then once). As for motivation to make a player do this perhaps make it that the final mission in New Game + will give you an Etheric Light instead of a mote of light.