Celestia and Luna married the mane six, now they have a harem and a honeymoon to deal with. In all honesty, happily ever after isn't all it's cracked up to be. At least there'll be room for orgies.
Have you ever gotten so drunk you forgot you offered the princesses' hoof in marriage to whoever brought your sister back? And how many 'es' there are in 'Princess'?
Set a few years into the future, six year old Pound and Pumpkin have a lot of growing up to do. They fight and make up, make mistakes and learn lessons, and love and protect each other as much as they get on each other's nerves.