Good I like changeling stories, and I have favoured it, but I think it needs a little more drama. I hope you start writing it. I look forward to your new chapter.
avi. or what it is called. considering the fact that Sin is sent to Ponyville several years after the event in season 2 finale, the six mares need to have matured, aka got married, in a relationship, have foals and so on. Personally I recommend having Rainbow being married to Soring, whit her as a wonderbolt and them having twins a filly and a colt. there are severel fics that talks about their children.
Also make Fluttershy and Big Mac be together. Twilight is a prude so she can stay single and Rarity is too high maintenance for any stallion to stay with too long anyway, and Pinkie is a hippy so she dosn't count but Applejack needs to have somepony to buck with. But if you can't figure out anypony good, then just mention that she has a husband without telling who.