But why? She's not really that good of a character. She was a complete jerk who committed so many heinous crimes against Equestria, and then it was all thrown out and she was immediately forgiven for everything she ever did. She wasn't slowly forgiven like Sunset Shimmer, no, IMMEDIATE forgiveness. Also, she doesn't have an element or a throne. I think she'll just become a semi recurring character, like Discord. He was reformed and he didn't join the mane cast. Adding a new member this late in the series is a bad decision. Not to mention, the 2017 movie synopsis doesn't mention Starlight anywhere and it says "Mane 6".