@Bonberjean  
Speaking of which, a ton of it ties back to Sunset and her attachments. Her destiny lies in both worlds, including Equestria’s to reconcile with Celestia.
 
And as for Twilight, I think you are underestimating an extended exposure to each other would be like. They are both completely Twilight Sparkle, but at the same time completely different people. The creators intentionally wrote them as very different. Pony Twilight is an expectancy and success driven person, while Human Twilight is a friendship and consequence driven person. Human Twilight wouldn’t do a quarter of the neutral stuff Twilight does on a daily basis, and Celestia is not a major part of Human Twilight’s life. They wouldn’t be able to relate to each other at all, which can lead to major development when trying to understand each other. I feel there was a good reason Human Twi became the first alicorn non-princess without needing a spell to force the others to share their elements with Twilight.
 
The Mane 6 deserve the opportunity to have the stage broadened for them without Celestia or someone’s constant safety net, and develop even further.

@Bonberjean  
Understandable.
 
I have mixed feelings about it myself, fusion is extreme, but the only reason I consider fusion is at this point is the Humane 7 have basically left the Mane 6 in the dust. :/
 
They have Sunset, they have the 7 elements now that Twilight has awakened. They have passive AND active Equestrian abilities now, and the 7 of them work together to keep the balance between Equestria and the Human world. The show? Its still constantly trying to justify the importance of Twilight becoming a princess each premier and finale, whether by her experiences or by her apprentices’s experiences.
 
I’m not saying they shouldn’t have well written meet up scenes, of course they should….but with the exception of the Twilight’s, what would be chemistry outside a few short scenes? RD, Fluttershy, Rarity, Applejack, Pinkie Pie, Spike….they all have the same personalities as their other versions. By the time Rainbow Rocks, Pony Twilight was quite literally catching up with her friends on the flip side. They are irrevocably the same people. On top of that, the high school setting meant that the EG’s don’t have any dream jobs in the human world at all beyond their hobbies that their pony versions already do along with their main ambitions. And the last movie established they have no intentions of being discrete with their growing magic, even though that’s obviously not an option outside the school if they only live in the human world.
 
(shrug) I’m just thinking about the show not degrading. They are constantly limiting their own options in the show, while the EG’s movies only expand. The show writers are deathly afraid to give Celestia a deeply personal episode, but Sunset coming to Equestria would allow that to happen.

@CronoM  
Fusion? nah… thats a bit too much  
what I can predict about it is:  
Twilights freaks out, Pinkies freaks everyone out, Rainbows challenge each other who is the cooler one, Rarities… make clothes I guess, Applejacks do nothing special, Fluttershys… do Fluttershy things
 

 
 
and Discord get confused about seeing two Fluttershys

@Bonberjean  
Indeed. A part of me hates to admit it, but Celestia, and in turn the show, have been so focused on forcing Twilight (or her half-baked apprentice) into being the only ones involved with major villains, that the rest of the Mane 6 haven’t had much time to grow strong.
 
Thorax’s memory of the Mane 6 kicking ass together is what the Equestria Girlss do now with Sunset, and all of their powers have been gradually growing. We don’t even know if the Mane 6 can use Rainbow Power anymore, while the Humane 7 are all uber powerful now. But they lack the experience the Mane 6 have.
 
I always wondered if, after a graduation scenario, the Mane 7 were forced to fight a villain threatening both dimensions, and the Mane 6 and the Humane Six fused to face the magical challenges in both worlds while Sunset finally ascended to nigh-Celestia level.

Dawww

I’m still waiting for an EQG movie that the EG have to go to the ponyville, encounter their pony selves and to some stuff to save the world