Suppose Sunset Shimmer had stayed in Equestria. Which Element(s) would she have wielded against Nightmare Moon?
If she had something besides Magic/Friendship, how would that have affected who else got which Element?
Would she have had the same team as Twilight? If not, who would have been there?

Articuno's thoughts:
If Sunset Shimmer stayed she would have earned Loyalty, for her new-found dedication to Celestia, not necessarily the crown. This could lays the foundation to a possible conflict of interest in the future if Celestia were to step down from the throne.
Sunset having the Loyalty Element would shift the Magic/Friendship to Rainbow for her unwavering dedication in her friends. Eager to get back to her work and unable to say No to Spike's gluttony, she would have had Big Mac guide her around town. He would tell the story of how he had a scholarship to Celestia's School for Gifted Unicorns(a misnomer) when his parents died within two months, she in child birth, he in an act of heroism with Applejack watching. He gave up his scholarship and higher education to work the farm in place of his parents. Applejack, ignorant of Mac's sacrifice, left for Manehatten hoping to pursue the sophisticated life, broke his heart, not that he ever let her know, Granny was the only one who ever knew. Big Macintosh would come to bear the Elements of Generosity. He would also come to push Sunset to leave Rarity quickly and avoid her harassment when she learned Sunset was from Canterlot.
Applejack, Pinkie and Fluttershy would play out in similar ways to Twilight with Big Mac running introductions to Pinks and Flutters.

I think a seventh element would have been added if sunset stayed. I think sunset would get the element of luck. Sunset shimmer has always been lucky no matter what. Princess Celestia student? Twilight said most unicorn can't even get accepted into that school and Celestia found sunset way before the she even came to school. Her fight took place on the last day the portal was open. The youngest and kindness princess was sent after her.

And maybe enough is enough.

5487574 Agreed on Sunset being a new Element, but I favor the Element of Empathy.

5727476 that is the seventh rainbow light ability. If sunset uses it a lot she could even predict what pinkie will do

5727503 But what does luck have to do with building and fostering a friendship? If you're going to introduce something new into a world, it's best to have it fit as closely into what's already there as possible.

5727526
I was just pointing out that sunset shimmer was very lucky. She was never to get into Celestia school for gifted unicorns. It was Celestia who brought her in.

It is commonly accepted by the fandom sunset's family is poor. They couldn't even afford train tickets. Most bullies come from poor families and pick on kids that are better off then themselves just to feel better about themselves. Sunset showed all the traits of that and in rainbow rocks she showed the same traits when a Bullie gets told off and punished.

I'm with sunset is empathy

5728846 ...where is it accepted by the fandom? This is the first that I've heard of the theory of Sunset's family being poor. I've seen stories where she's an orphan taken in by Celestia, stories where she had loving parents and was orphaned, and various others, but this is the first I've heard of stories where she was of poor upbringings.

And most bullies coming from poor backgrounds? Bullshit! Bullies can AND DO come from all sorts of backgrounds! And there are plenty of explanations for Sunset becoming a bully that don't rely upon her coming from poverty.

I'm not saying she didn't - we have no information on her background before she was Celestia's student in any of the animated material or comics - but just because some people believe something doesn't make it a fact.