Madoka = Fluttershy  
Sayaka = Pinkie  
Homura = Twilight  
Kyouko = Rainbow  
Mami = Applejack  
Hitomi = Rarity

No  
Pinkie Pie = Madoka

@Background Pony  
Not to argue your point about who fits who best, but Rainbow Dash is not exactly a complete jerk or without a soft side either. And while Kyoko’s cynicism is understandable it doesn’t justify everything she did before she found out the truth.

If Rainbow Dash is put in Sayaka’s place, it would be fitting as to deconstruct her Element of Loyalty, same way the Madokaverse deconstructed Sayaka’s lingering loyalties. Sayaka was torn apart between her love for Kyousuke, her loyalty to her friend Hitomi, and her loyalty to the duty of Magical Girls as “knights in shining armour”. The Element of Loyalty is one of the most vulnerable Elements, considering how the Madokaverse Crapsack/Real World is full of betrayal.
 
And instead of trying to fit Pinkie in (when either Discord or Trollestia makes a more manipulative Kyubey), I prefer her to be a Charlotte-like witch based on the episode “Party of One” combined with “Cupcakes”. Pinkamena Diane Pie, the Witch of Parties. Her element is Laughter. It is ironic that she loves parties yet is divorced from the definition of a party, that is an actual social gathering of people. She is eternally trapped as the only participant, her inner loneliness concealed and compensated for by delusional animations of nonliving objects, and the occasional postmodern humour used in laughing at herself and the world. Her maze, while seeming like a sugar bowl at first, will in its inner depths include ironic and sinister references to her past life. Though she is capable of creating infinite amounts of any dessert and decorum she desires, she is unable to acquire real ponies that she love the most, both to have as a partner to satisfy her lonely parties of one, and as the crowning ingredient for her infinitely-delicious Cupcakes. That said, I want Pinkamena to be able to communicate and have a sick sense of humour, as to make this Witch more sinister and Urobuchi-like than the Madoka witches, while Rarity/Mami’s death should be even more horrifying.

@Background Pony
 
But Kyoko is only putting that tomboyish facade not because she’s like Rainbow Dash but because the truth made her cynical. Kyoko isn’t a complete asshole, she simply knows the “food chain” nature of the universe, and is trying to be honest about it to the more idealistic denialist characters such as Madoka and Sayaka. After realizing the truth about how Kyubey turned them into liches, she even helps and teams up with Sayaka, narrating about how she became that way (her conservative father went insane and committed murder-suicide on their entire family when she revealed her identity)! Being the Element of Honesty, I think Applejack would make a better Kyoko than RD, and since the Madokaverse is a crapsack world, her element of honesty would logically lead to a more cynical mindset (and witnessing her beloved Apple family driven to madness/suicide/death by her doing is also a great source of additional cynicism for her).

@Background Pony  
In terms of personality Rainbow Dash fits Kyoko’s attitude way better than anyone else would, and I like Pinkie as Sayaka (someone who goes crazy when their idealistic illusions and delusions are shattered) is perfect.

@Background Pony  
We’re talking personality-wise rather than VA-wise. That’s why Fluttershy is Madoka (selfless Moeblob, keep in mind that she only uses the manipulative Stare when others are in danger, a lot like Madoka’s self-sacrifice to save other Puella Magi), while RD is definitely Sayaka (blue-themed, idealistic and reckless). Although Pinkie does not really have a clear equivalent, and I myself prefer Trollestia as Kyubey.

No, just no.  
Rainbow Dash would be Kyouko (do I even need to explain this one).  
Pinkie Pie would be Sayaka (Extremely cheerful, attached to her loved ones, unexpected gloomy side).  
Rarity as Mami is okay, though.  
Twilight as Homura too, sorta,… because of the whole time travel thing, even though she lacks the motivation that Homura had.  
AJ as Madoka makes some sense to me, AJ may be brave overall but gets easily scared regarding the unknown, and needs a lot of pushing/pressure to get things done and can be a tad insecure.  
And after the whole japanese VA thing, Fluttershy as Kyuubey wouldn’t surprise me :P She’s adorable but can be quite mind controlling if she wants to, with the whole stare thing, getting others to do what she wants and stuff so…

Rainbow Dash: There’s no way that I’d regret this!! (definitely an idiot)  
Applejack: This gal’s dead!! (magical lich)  
Fluttershy: I don’t want this…

@LordGenbu21  
This!
 
FS: “I want you to form a contract  
with me and become magical  
girls… if you want…”

i hope more kyubey/fluttershy crossover after the dub begins.

@Justy
 
Yeah. Nice try, but I’m not feeling the sass.

@Background Pony
 
I can’t tell for sure. It probably manifested sometimes around adolescence, but we were never shown that part. Sorry I couldn’t be of more help.
 
@Dumb Rock
 
Don’t be so hard on Chaos, he tries.

@Justy  
Since when is Rarity a cunt?

@chaos15
 
Kind of. It’s got a nice sound to it.

MADOKA MAGICA! (FAN GIRLISH SQEUAL)

Great, a good pic with an awful comment.

@Justy  
I think you really like the word cunt.

Nah, AJ’s not a cunt. Rarity should be Kyouko.  
RD’s just enough of a cunt AND a reckless idiot to be Sayaka. Not sure about the tragic part.  
FS is certainly useless enough to be Madoka, at least the “current timeline” sheltered dipshit Madoka.  
Twilight is the only one with a lick of common sense, so Homerun is the only choice.  
AJ as Mami would do, dies soon enough to not really matter (except being a cunt and a psychopath later on, maybe Rares could do a double role and we can dump AJ entirely?)  
Pinkie is totally batshit enough to battle entropy by torturing teenage girls to death since the dawn of times.
 
Yep, this could work.