Description:
Little thing I found that goes over why if there is truly an addition to the Mane 6, Starlight would actually be a good choice, and Sunset be bad in the long run. Putting spoiler tag just to be safe
tl;dr: Starlight has plenty of potential for growth and interaction over an arc, Sunset is already developed and would have hardly anything to go on plus would be an essential Twilight clone with a new paint job.
