I'd really love to have a Mother's Day episode with all of them (well, it'd be Granny Smith with AJ for obvious reasons).

Maybe something like each of them switch a mother (Rarity's with Granny Smith, Dash with Cloudy Quartz, Twilight with Cookie Crumbles, Fluttershy with Windy Whistles and Pinkie with Mrs. Shy or some other combination thereof).