Because Twilight Sparkle was involved, there was a list. That was why Cadance had asked Twilight to be involved, to help keep things organized.
Cadance knew Twilight was very smart. And to balance that, Cadance would have some of the emotional issues covered better than Twilight could. Really, with both of them involved, what could go wrong?
To indulge and encourage Twilight, Cadance had asked to have several of those big chalkboards on wheels brought in. That was what servants were for, after all! Cadance wasn't sure how Twilight managed without an entire palace staff of servants and guards and any other kind of assistance might happen to be needed.
(Sometimes Cadance wasn't sure whether she should feel sorry for poor Spike, or in awe of his ability to cope all by himself with the needs of Cadance's high-strung niece. But today, Cadance had asked to let Spike amuse himself freely in the Crystal Empire. She thought he surely deserved a day off.)
Cadance looked up at the chalkboard.
Princess of
Sun
Moon
Love
Friendship (is magic)
"The question," Twilight said, "is what comes next? Is it some kind of simple logical progression? Or is it a matter of what Equestria most NEEDS next?"
"Hmm," Cadance said. "What DO we need next?"
Twilight stared at the chalkboard, looked at Cadance, and looked back at the chalkboard. "Search me. I didn't even know we NEEDED an alicorn princess of love all that much."
"Hey!" Cadance said. "Love is important!"
Twilight said, "Maybe it ISN'T about Equestria at all!"
Cadance replied, "The Crystal Empire's protective magic depends on love! So that makes sense!"
At the same time, Twilight said, "I'll bet it was for the changelings! The Crystal Empire generated SO MUCH love that it helped Thorax to turn good, and he reformed all the other changelings! The CHANGELINGS needed an alicorn of love!"
Cadance's head tilted slightly, "You think I'm supposed to be the princess of the CHANGELINGS?"
"Well, sure. At your wedding, Chrysalis took your place for weeks, and hardly anypony even noticed. Surely the next logical step was for you to FINISH changing places with her, and you would rule the changelings."
Cadance looked at Twilight, then at the blackboard. "Huh. I don't think Chrysalis would want to go along with that."
"It would have been the logical next step, though. With thousands of changelings invading Canterlot, sooner or later one of them would have found you, even in the old mines under the city. You radiate so much love, I don't think you could have KEPT them from finding you."
Cadance looked alarmed. "You don't think I COULD hide from them? No matter how hard I tried?"
Twilight nodded. "And you're just such a wonderfully kind, loving pony, you probably couldn't help but be a good influence on them. The Changeling Love Reform would have happened years earlier, before Thorax started the reforms in our timeline.
"Instead of the princess of one small city that we call an empire for some reason, you would have become the queen of an entire species. Their loving leader, teaching them right from wrong, making sure their children were raised properly from the beginning. The mother to an entire nation."
Cadance looked thoughtful. "Huh. You really think I could have done that?"
"I do!" Twilight said cheerfully. "It's a shame low-level changelings didn't find you when they were invading Canterlot, or it really could have happened." Twilight blinked. "Cadance, I guess I'm a terrible influence."
"What? How's that?"
"Because I rescued you and kept you safe from changeling soldiers." Twilight sighed. "Well, I meant well."
"I liked being rescued!" Cadance insisted. "I think Shining liked it too."
Twilight shook her head. "As a royal guardpony, Shining would understand that sometimes he has to suffer so other ponies can be protected. And reforming the changelings early would certainly help protect everypony." She sighed again. "Maybe later I can ask Starlight Glimmer to do a little experiment with me about this, and we can make you a full queen retroactively."
"But what about Flurry Heart?" Cadance insisted. "What's SHE the princess of?"
"My current theory," Twilight said, "is that every princess is the princess of at least two things. Celestia is princess of the sun, but she's also a princess of the day, and of light, and of acting motherly."
Cadance opened her mouth slightly, as if to interrupt.
But Twilight continued, "Luna, of course, is princess of the moon...but she has stars twinkling in her mane and tail. So is she princess of the night, or of stars, or some of both? Maybe both."
"There's dreams," Cadance interrupted.
"Of course!" Twilight said. "See? Multipurpose! A true princess is like one of those knives with all the different little tools that you can fold out of it."
"You're saying you and me are both Swizzlestickland multitools?"
"Sure! That's a great analogy. I'm the princess of friendship, and of magic. And of books, I guess. That's three things right there."
Cadance looked like she'd guessed what came next, and she didn't like it. But--" Cadance started to speak, but stopped herself.
"But what?"
"What am I the princess of?"
"Love."
"Love and WHAT ELSE? If I'm only the princess of one thing, that doesn't seem fair."
"Cadance, Cadance. You're not ONLY the princess of love. You're also an excellent babysitter. And we call you the princess of the Crystal Empire, even though the actual territory you rule is very, very small. I mean, there are mayors in Equestria who rule more land and more ponies than you do."
"I see." Cadance sounded a little peeved.
Twilight clapped her forehooves together. "I've got it! Babysitting, an undersized territory...put those together, and what do they spell out?"
"I don't--"
"For an alicorn princess, they spell underachievement!"
"What?!"
"You're the alicorn of underachievement, Cadance! A princess for the regular ponies. When you were in school, what were your grades like?"
"When I was little, I didn't even GET to go to school. So ever since I moved to Canterlot, I had to play catch-up ever since--"
"See? It all fits!"
Cadance snorted. "Well, I've done ONE thing you haven't."
Twilight looked as if she hoped to hear good news. "Good! What's that?"
"I'm a mother. Have YOU ever been a mother, Twilight?"
"I hatched out a baby dragon when I was just a foal. I think he's turned out very well. How old were YOU when YOU hatched out your first child, Cadance?"
"I didn't HATCH little Flurry. Don't you know where foals even--"
"I'll bet you were a lot older than I was, Cadance, when you finally had your first child. See? Yet again, the princess of underachievement!"
Cadance said, "My daughter can do something your Spike can't do." She walked out of the room.
Twilight started to follow after Cadance. "Cadance? Where are you--"
Cadance reentered the room, carrying a familiar foal. "Flurry Heart!" Cadance ordered, "Zap the purple thing! Zap the purple thing!"
"Ga gwaa gurgle blabble!" Flurry Heart made adorable faces at her aunt Twilight.
"Hmm," Twilight said. "Your daughter really is useless, isn't she?"
Cadance protested, "She's less than two years old! How useful do you think she should be?"
"When Spike was her age, I already had him scrubbing floors and carrying books, and doing other useful work."
"You've always treated that poor little dragon like a slave. Don't you feel ashamed?"
"It's not MY fault you can't get your children to do any chores, Cadance. Let's face it."
"Face WHAT?"
"As an alicorn you're an underachiever, and as a mother..."
"As a mother, what?"
Cadance noticed Twilight looking at something behind her. Cadance turned around, to see Shining Armor arriving.
Twilight grinned, and hugged her brother. "Hey, BBBFF!"
"Twily! What were you two just doing?"
"Oh...just figuring out a few things. Like, unlike other alicorns, so far Flurry Heart seems to be, on a a regular day to day basis, basically useless. So far, she's the alicorn princess of nothing. And Cadance, as a mother..."
"As a mother, what?" Shining asked.
"I guess Cadance is about average."
Shining turned to his wife. "I'm sorry, Cady. Sometimes Twilight gets in these moods where she thinks everything should be perfect, all her tests should be a hundred and ten percent out of a hundred, even the smallest normal pony imperfection will cause doom and make everypony have to go back to magic kindergarten...you know how she can be."
Cadance smiled, stifling laughter. "Yes, I know. I've seen it for myself many times. I babysat Twilight so much when we were younger."
"That's true!" Twilight said. "You WERE a good babysitter. You were such a good babysitter, you must be a good mother too."
"Thank you," Cadance said. Her body wiggled with the effort of not giggling at her perfectionist niece. "So I'm not a terrible mother after all."
"Of course you aren't. But I am worried about one thing."
"What's that?"
"Flurry Heart can't talk, doesn't do any of the chores that Spike did when HE was two, has such erratic magic...I wonder what's wrong with her?"
Shining Armor laughed. "Nothing's wrong with her. She's just a normal little foal, that's all."
Twilight sighed. "I suppose that's true. She's just normal. But when you look at who she's related to...an Equestrian Guard captain, the most magically gifted, intellectually brilliant, and purplest unicorn of our generation...and you know what our parents are like, Shining. And to raise a pegasus who turned into an alicorn, Cadance's parents must have been doing SOMETHING right. They must have been exceptional in SOME way."
Shining said, "I don't see where you're going with this."
"All I'm saying is, are you sure Flurry Heart isn't adopted?"