To proponents and supporters of the "Equestria Girls is set before Friendship is Magic" Theory/Headcanon.

[Newman1651 35]

Prepare yourselves for the almighty Wall of Text...

If that really was the case, then Generation 4/FiM would have gone down the Adventure Time path. Like how Adventure Time was originally not going to be post apocalyptic but the creators went with that notion after the episode "Business Time" since they thought it made the world of the show look post apocalyptic.

When I mean going down the Adventure Time route, it also extends to the condition of pre war ruins, relics and even dead bodies. Still recognizable and even in surprisingly good shape after  thousands of years. There was even an episode where Finn and Jake restore a pre-war Truck that was 1000 years old back into working order. Even the skeletons of dead humans from the pre-war years are completely intact and haven't disintegrated into dust. In some cases, their clothing is still intact as well.

As with the land of Ooo, relics of Human civilization would have been littered across Equestria and beyond. Things such as bits of ruined human infrastructure poking out of the ground or in forests and jungles. Or even deep beneath the sea. Some ponies in certain areas would even be using carts and wagons fashioned from the hulks and shells of ancient automobiles (ex: a wagon fashioned from the shell of Human Flash Sentry's car).

The apocalypse that wiped out Humanity as well as the the age of the ruins of their civilization would predate the existence of Grogar. by thousands of years. And who knows, Grogar might have something to do with the destruction of the Human race. Much Like Adventure Time's Lich. He'd likely be re-written as the pony equivalent to the lich had they gone with the "EqG happened before FiM" decision

The Likely cause would be that the magic leaking into the Human "World" eventually flowed freely into the Human world after the interdimensional sluice gates opened. resulting in the human counterparts gaining the powers of their equestrian counterparts and equestrian flora and fauna invading the ecosystems of the Human world and drastically altering them. When that Happens,  It will destroy everything and everyone.

Humanity is unprepared and unworthy to handle Equestria's magic as it inundates and floods their world in great quantities of Biblical proportions. When every Human in that world gets the powers of their equestrian counterparts, they would likely abuse their abilities to high heaven. That's the general theme of EqG antagonists and villains. Using magic or magical items from Equestria and abusing it for their own gain.

And worse. Imagine the Human counterparts of Villains from Equestria getting the powers and abilities of their equestrian counterparts. Like a Human Chrysalis gaining the power to Shapeshift, a Human storm king gaining an object similar to the Staff of Sakanas as well as his magic draining powers and ability to calcify (Turn to stone) his victims, Human Sombra gaining his dark magic and ability to mind control vast amounts of people en masse, Human Tirek gaining his magic stealing powers of his counterpart, and finally, Human Grogar gaining his goat counterpart's ability to create monsters.

This also extends to characters who's equestrian counterparts have villainous corrupted forms. Like Principal Celestia and Vice Principal Luna gaining the powers to move the sun and moon as well as the risk of them transforming into Nightmare Moon or Daybreaker. one capable of Burning the world and the other capable of freezing the World in eternal night. All of this just contributing to the annihilation of the human world and the Human race as it spirals down into an inescapable swirling mass of chaos and devastation.

.As Humans have a history of wars and violence in comparison of the otherwise peaceful equestrians, an apocalyptic world war erupts that involves magic and nukes. or even Nukes imbued with magic (Megaspells?). Something like the Equestria Girls equivalent of the Great Mushroom War. It will be unlike any human conflict throughout history and would even supersede World War 2 as the most destructive conflict in Human History by the Tons.

And When I mean Bad, I mean bad to the levels of the Seven Days of Fire from the Nausicaa Manga/Anime.
This at first, brings about the collapse of industrial civilization due to the convenience of magic in people's lives and later on, the extinction of Humanity as the remaining survivors are killed by the hostile flora and fauna of the now magical Earth.

Long story short:

 

Just imagine a region in Equestria that used to be Human world Canterlot in EqG. Like an entire Kingdom built among it's ruins. Just imagine seeing some buildings or landmarks recognizable from the EqG spinoff. Some of them being re-purposed as buildings or part of a building in a town or village in the Kingdom. The centerpiece of these ruins being Canterlot High. Being used or even modified into a "Castle" by it's pony occupants.

The Ruins of Crystal Prep would modified to be more like a fort or citadel for the kingdom's army and military.

The Metropolitan section of Canterlot city that was seen in the "Super Squad Goals" would be these nearly unrecognizable ruins 
being a literal concrete jungle. The ruined skyscrapers becoming these huge overgrown canyons towering from a distance.

Another town would be set up amidst the ruins of the Film Studio seen in "Movie Magic:

Another place for one of these towns or villages would be a pony settlement built among the ruins of the Equestria Land Theme park from "Rollercoaster of Friendship". The only recognizable structure being it's Ferris Wheel. Having been converted into a Windmill.

Only Twilight Sparkle and Starlight Glimmer would be able recognize ruins of such structures as Canterlot High as well as the other ruins of locations they've both been to during their time in the Human World. To everyone else, they don't even know the origin or what the true nature of these structures are. I could definitely see a "planet of the apes" moment with Twilight.

And to top it all off, Imagine Twilight coming across the ruins of what was once Sunset Shimmer's Flat and finding her journal in the ruins and getting emotional upon discovering it.

And I have a second question. How would Equestria react and respond to  watching their Magic flowing freely into the Human world and wreaking havoc in that world as well as threatening to destroy and wipe out the human race and civilization as their human counterparts would gain their magic and leading to an apocalyptic magic war occurring as it dawns upon the ponies and to some extent, Starswirl, that the Humans are a violent species with a history of wars and conflicts and that they're not worthy to use Equestria's magic due to their cruel, violent, and selfish nature.

That and also the possibility of the human counterparts of villains in the show gaining the powers of their counterparts and helping in flushing humanity and their industrial civilization down the pipes.

[cuteycindyhoney 13,282]

Equestria Girls, in my opinion, runs parallel to the pony's world. Twilight visited the human world several times. She also has experience in time travel. She would have noticed if she traveled in time, instead of just crossing to another world using Star Swirl's mirror. The mirror he created and specifically used to send the sirens to a different world, with no mention of a time travel element. Why would he send them back in time thousands of years, and then say he sent them to a different world? Granted they were on the human world for a long time. It just took them that long to slowly regain their power. The events in the first Equestria Girls movie took place when Sunset stole Twilight's crown and crossed to another world. She didn't time travel. Another thing. Sunset's book allows her to communicate with Twilight in Equestria. It would need magic on a whole other level of power to be 'real time' communicating over thousands of years.

Edited April 27, 2020 by cuteycindyhoney

[Newman1651 35]

20 hours ago, cuteycindyhoney said:

Equestria Girls, in my opinion, runs parallel to the pony's world. Twilight visited the human world several times. She also has experience in time travel. She would have noticed if she traveled in time, instead of just crossing to another world using Star Swirl's mirror. The mirror he created and specifically used to send the sirens to a different world, with no mention of a time travel element. Why would he send them back in time thousands of years, and then say he sent them to a different world? Granted they were on the human world for a long time. It just took them that long to slowly regain their power. The events in the first Equestria Girls movie took place when Sunset stole Twilight's crown and crossed to another world. She didn't time travel. Another thing. Sunset's book allows her to communicate with Twilight in Equestria. It would need magic on a whole other level of power to be 'real time' communicating over thousands of years.

I'm referring to peole who actually believe this theory and hedcanon I'm entertaining to.