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.
When Celestia dares Luna to lick a pole out in the park, promising her that she can be the big spoon when they snuggle that night, Luna doesn't have to think twice. Besides, it's only for a second, right?