I’m going by my little bit of headcanon on this, but IF Starlight and Sunset were to become the mane 8, I would say that Sunset would represent the element of forgiveness and Starlight would represent the element of understanding. Why? Take a look at Sunset in Friendship Games, she FORGAVE dark Sci Twi for what she did, step further into the season 5 finale and Starlight began to UNDERSTAND the way her actions were and would effect/affect the lives of others and that she shouldn’t blame herself for not gaining any real friends all because of a cutie mark. Again, it’s my own headcanon.
Not a bad idea. :)