I finished reorganizing my chapters. Don't worry -- nothing's actually been lost, but some of the parts of the original overly-long Chapter 13 "Waiting for the Princesses" have been moved up beyond my publication horizon. I think you'll find that the character development of the Mane Five Minus Twilight Plus Spike don't clog the story as badly now.
The tentative new chapter structure of this section will be as follows -- published chapters in blue and unpublished in red. I'm leaving "Pinkie, Dancing" back in unpublished status until I write the intervening three chapters, but I haven't dropped it from the story -- it's structurally essential!
Chapter 13. "Rainbow's Boast and Fluttershy's Plan
Chapter 14. "A Bad Little Filly"
Chapter 15. "Applejack's Regret"
Chapter 16. "A Trip To The Library
Chapter 17. "Rarity's Reverie"
Chapter 18. "The Sun Mare and the Twister"
Chapter 19. "Pinkie, Dancing"
Chapter 20. "Sweet Years of Maidenhood"
Chapter 21. "Discord, Deciding"
Chapter 22. "Luna's Betrayal"
Chapter 22 isn't the end, but is the last chapter before the climax and denouement, so it will be most of the way to the end.
I also need to move the Notes around so that they pertain to the right chapters. If you spot misplaced Notes, don't be shy to comment or message me on it.