Well, according to the premiere it looks like we know what Starlight Glimmer’s endgame will be in the show once Twilight and her friends take over Equestria. She will live permanently in the castle and be the new head-mare at the School of Friendship. I think this fits her perfectly.  
She gets to guide others in the magic of friendship the same way Twilight guided her. Not to mention she gets to live permanently in the very castle in which she both, destroyed friendship (using the map in The Cutie Re-Mark) and was taught the magic of friendship. No better ending for her journey honestly in my opinion.