king of all appleshy

Rainbow immediately addresses the elephant in the room and all but volunteers to form a union with Luna; something she does partly to prove she isn't afraid of anyone or anything, but also because… look man she said she was sorry and she's gonna start her new rule with everyone against her - someone has to be there for her. Celestia especially approves of this union, as, even if these marriages are largely political, the element of Loyalty would make a true companion for a pony like Luna. Despite that, I think their start would be difficult, given all the ways the two are opposites… but ultimately flying by moonlight is just as nice as flying during the day, and the long stretches of peaceful nights give them plenty of time to get to know each other.

Cadance solves the unbalanced issue and forms a union with both Pinkie and Fluttershy. There's no limit to virtues that are compatible with Love, but Laughter and Kindness just have that little something extra that catches her attention, nevermind how stinkin cute they are. All three take to their new marriage well. It’s especially helpful that Pinkie and Fluttershy have a pre-established friendship that could easily remain platonic, or turn romantic or queer-platonic; there’s also the fact that Cadance herself was once a humble pegasus raised by earth ponies before being thrust into this royal life, which could be why they caught her eye in the first place. 

(Shining is still here, as someone needs to train these girls in the art of guarding, and their relationship is still active (although PinkieShy would not be considered his wives); bc if there’s one thing I’m going to do with the princess of love, it's show off some poly pride!)

Twilight would, at this point, ““have her choice”” between Generous Rarity or Honest Applejack; either would be fitting for her new title as the princess of Friendship, and both are good ponies who she could rely on. However, given just how much Twilight’s life is about to be upended with new, well, everything - ultimately Rarity turns out to be her best match. She’s generous with her patience and tact in a way AJ isn’t quite, and more importantly she understands the ins and outs of the high class, making her a real asset in Twilight’s transition to royalty. Nevermind that the two were maybe already a little smitten before their union even took place…

This leaves Applejack sort of “auto-paired” with Celestia. At first Applejack seems like a horrible choice for a princess who is practically a queen, given how very little she knows about this life, and the way the upper class look down on her, but it ends up that her more open/harsh honesty that would have maybe been too much for Twilight in her new role is actually perfect against Celestia. It takes Applejack a bit to learn how to hold her tongue in royal public but she learns to play the game in her own way, and her willingness to speak openly and bluntly with Celestia - in private - is so refreshing to Celestia, who hasn't had a pony tell her like it is in ages. That said, i think this learning curve takes quite some time to even itself out, and in the beginning they spend a lot of their marriage clashing with each other, though ultimately i see Applejack as a respectful enough horse that her southern charm does just that, charming the princess in a way she couldn’t expect.