I've been hearing people theorising that she will join the Mane Six as a main character for season six. I'm a bit skeptical about this, but If this does happen then I guess it would be a case of this trope. If this did happen how would you feel about it?

I am honestly divided.

One, that backstory was so bare bones... They need to really, really expand that. Show how hurt and misguided she became over the years, show us her shock and disgust at getting her own cutie mark.

On the other hoof, nearly all the cut content in Friendship Games had to do with Sunset Shimmer being homesick, and wanting to return to Equestria. As a huge Sunset fan, as much as I want Starlight's backstory to be fleshed out, I'll be damned if she takes what should be Sunset's place.

4890880
Oh for the love of all that is holy!

I'd rather see her go on her own merits than join the band of Sues!
Plus, her backstory was a steaming pile of lazy writing. So much wasted potential.

4890880 That does seem to be what the ending, as well as the line "we can't just send her on her way" seemed to imply. Although we won't know for sure until season six begins. (or at least the season trailer)

Would adding her to the group be a good or bad thing? It all come down to how the show staff handles it, which it is way to early to tell. I for one am looking forward to finding out. (just like any other change to the status queue)

As to the fear of her replacing Sunset; even in the deleted scenes she decided not to move back to Equestria, so there would not be any replacing anyway.

I really hope she does. It'd be nice to have a battle mage in the party for once. Though I hope it'll be an excuse to bring Trixie back. Maybe to find out Twilight is friends with Starlight and make her jealous or give her the drive to become better. Honestly I feel that the CMCs should have had a hand in her reformation.

That'd be so cool the three fillies turn the villain into a good guy by helping her realize cutie marks can mend broken relations, such as the case with them and DT and Silver Spoon. But to have her in the main party group? I like the idea, but I know in my heart that they'll never do it.