@Background Pony #85F6  
Think more along the lines of alternate or branched timelines.

@CMC Scootaloo  
You mean the G4 franchise has two universes? One pony world and one human world?

Seriously! When will there be more Equestria Girls?

So… when will they announced ore Equestria Girls including a proper finale?

@Background Pony #2B47
 
I didn’t say “in the same world”. I said there are two different versions of the Siren trio that exist in two different parallel universes. One we see in My Little Pony: Friendship is Magic, the other we see in EQG.  
How much you dislike the siren issue of “Fiendship is Magic” (I dislike it, too) doesn’t matter.  
There’s the fact that there are two different versions of the events when Starswirl defeated the Sirens floating around, one from EQG, one from My Little Pony: Friendship is Magic, and that fact can’t be refuted.  
The sirens seen in EQG and the sirens seen in My Little Pony: Friendship is Magic are not the same sirens and each trio was sent/banished to a different place.

@CMC Scootaloo  
Why you mention this terrible comic, seriously, in wchich Star Swirl was made as pathetic loser? I’m pretty sure it’s not considered canon at all (except the last pages when the become humans in EqG world).
 
There are no 2 versions of sirens in the same world. The story in Rainbow Rocks was just a simplifiied version of a story of sirens in Shadow play. These are the same sirens transported from this universe to another.
 
We don’t actually know that there will be human dazzlings from EqG world.

@Thunder_Arch
 
No, it would still be an alternate universe then. By that logic, you would have to see the Walter White pony from “Grannies Gone Wild” as a pony who actually lives in Equestria, too. But we know it’s just a reference to another TV show. The chance that a pony who looks like Walter White lives in Equestria is little to non-existent.  
Characters from other shows who appear in My Little Pony: Friendship is Magic as ponies aren’t part of the script, they’re inclusions by the storyboarders or animators to make a joke or to reference something popular for the sake of fanservice. Which was the case when Flash Sentry was suddenly seen with a speaking role in “Three’s a Crowd” and if Sunset Shimmer where to be seen, then it would be the same.  
Although, for such appearances of Sunset Shimmer and Flash Sentry, there is a different and more complex possibility:
 
Since EQG and My Little Pony: Friendship is Magic show the audience two different universes, the hypothetical appearance of Sunset Shimmer in the latter would then simply be the Sunset Shimmer of that universe, not EQG’s universe. Same goes for Flash Sentry.  
There are also two different versions of the Sirens, after all. One version was seen in that one EQG comic that they included in “Fiendship is Magic” and who were sent into the human world from EQG by Starswirl after some kind of magical music competition in ancient Canterlot.  
While the versions of the universe that is seen in My Little Pony: Friendship is Magic contacted Stygian, seized control of his village and the ponies living there, were eventually fought by the Pillars of Equestria in Stygian’s village (as opposed to Canterlot) and sent away by Starswirl through a magical portal that leads who knows where.  
And while every EQG fan celebrated the Season 7 Finale and “Legends of Magic” for supposedly acknowleding EQG’s existence, it was, for me, a reason to celebrate that the theory I already had since Season 4 got confirmed by Season 7’s finale.  
My Little Pony: Friendship is Magic and EQG are entirely separate.  
And since they are separate, that means that there are not only two different trios of Sirens (the one that got sent to the human world in one universe and the one that attacked Stygian’s village and got banished to an unknown world in the other one), but that there also have to be two different Sunset Shimmers (pony) and two different Flash Sentrys (pony).  
With their human counterparts living in yet another, third universe, in which ponies aren’t ponies, but humans instead.
 
So, long story short, if Sunset Shimmer were to be seen in My Little Pony: Friendship is Magic, then it wouldn’t be the Sunset Shimmer that you’ve seen in EQG and that went through the mirror to the human world, it would either be a mere cameo by a storyboarder/animator or it would be the Sunset Shimmer from the universe of My Little Pony: Friendship is Magic.

@CMC Scootaloo  
Well if she happened to appear like the new pony said, it wouldn’t be an alternate universe anynore, since it would be in the season 9 finale

@Background Pony #2837  
Now that you got that off your chest can you sleep easier tonight?

@The New Pony  
Not gonna happen.

@The New Pony
 
That wouldn’t even bother me too much, even though I hate EQG. Since EQG is an alternate universe anyway, it would be a mere background gag that can get easily ignored.  
Also:
 
 

@The New Pony  
That would most definitely work for me.

Imagine after all these denials that Sunset would make an appearance in 9 your watching the last episode and its a Star Wars like ceremony going on honoring the Mane 6. The camra pans over focusing in then BAM! Sunset is seen in the crowd, like Twilights parents during her coronation, she doesnt even have to speak. That would have the audience roaring and give me some sort of peace!

@CMC Scootaloo  
I personally think both have equal potential :)

@Twilight_Shimmer
 
That could be explored in one or two more specials/movies. While all the potential My Little Pony: Friendship is Magic still has with everything we haven’t seen of Equus so far and with all the ponies we know next to nothing about could go on for another nine seasons, if Hasbro would let it.  
It’s still a questionable claim to say that EQG has more potential.

@CMC Scootaloo  
Like the open fissures between worlds? Why so many Equestrian Artifacts are finding their way to the human world? juat to name 2

@GrapefruitFace  

 
So, you’re saying that the potential of EQG isn’t bigger than the potential of My Little Pony: Friendship is Magic.
 
 

 
And now you’re saying it is bigger. That is one heck of a contradiction.
 
 

 
Like what?

Don’t cry because it’s ending. Smile because it happened.

@Background Pony #4F91  
Looks like Habros gonna pull you in kicking and screaming.

@eagc7  
Anything but a reboot from hasbro, please. I want the series to continue the way it is. It’s be a great opportunity to expand some of the supporting characters a lot more background to their characters

@Background Pony #631E  
I think its possible they are ending the current iteration of EG and it wont be picked up by another studio.
 
I think this has to do with G4 ending and Hasbro may want to reboot EG so it can be tied to G5.

Why are we still here just to suffer every night I can feel my leg and my arm even my fingers the body I’ve lost the comrades I’ve lost won’t stop hurting it’s like there all still there you feel it to don’t you

@Twilight_Shimmer  
Well this wouldn’t be the first time Hasbro have ended a series with plot threads left unresolved. Transformers Animated anyone?

@CMC Scootaloo  
I’m not saying it has more potentional than FiM. I just think that EQG is still in it’s infancy. Yes alot of FiM’s world has not been explored but EQG has a lot more left unanswered and explored. I feel like EQG still has a lot more fresh content to be explored whilst FiM has had 9 seasons of 20 minute episodes over around 10 years.
 
That’s just my thoughts though.

@Background Pony #83D0  
THANK YOU! That would be the perfect ending to the series! The Rainbooms graduating from high school and Sunset debating whether or not to stay in the Human World or go back to Equestria.