@platypusmac
 
As long as those keys weren’t in the library when it was destroyed, then maybe.

@Evowizard25  
In short, IDW basically has created the key to inter-series crossovers galore.  
MLP-Godzilla, MLP-Popeye, MLP-Transformers and even any kind of other crossovers, with or without MLP.  
You can hear the Ka-ching in the IDW publishers’ minds from here.

@Evowizard25  
And yet again, everything comes back to the TV show Sliders

@Background Pony #F58E  
I think Twilight should learn the secret of traveling police booths!! :O!

@Ping_chan  
One mirror for one world? Nah, more like One Portal to infinite amount of worlds!
 
P.S. And everyone knows that police phone booths nowadays can’t travel between worlds. It was available in the “past”, but not anymore.

@Ping_chan  
Technically, you could crossover any world, cartoon, game with Equestria, thanks to the mirrors, and it’d be canon.
 
It’s like Bioshock Infinite. Parallel worlds allow for anything to happen.

@Ping_chan  
Nope, we have our access to Rainbow Rocks. /theory

And then she opens a portal to other universes by accident and horrors beyond imagination spill forth.

I just realized something, if Equestria Girls and this latest IDW comic arc were made possible due to Starswirl the Bearded experimenting with magic mirrors..  
I wonder what could happen if Twilight were to pick up on Starswirl’s research and actually try to build her own magic mirror?  
What new crazy backwards world could Twilight Sparkle visit if she made her own mirror?  
Or instead could Twilight build some other sort of magic traveling device? Some other common item that could open up a portal to somewhere or sometime else? A door? A table? A phone booth? Or maybe some sort of phone booth looking police summoning safety container?

AJ, get your head off my royal heinie.

AJ sayin’ the truth.

My thoughts exactly, AJ….

“Luna, this bitch has a problem with books. We were trying to get her clean. STOP ENABLING HER ADDICTION.”

Basically what Aj said.