1- Celestia recounts her younger days.
Taking a cue from her sister, Celestia takes a more proactive approach with young fillies. Though she chooses Silver Spoon, Diamond Tiara, and Pip.
2- Scootaloo's parents.
Or a lack there of. Interesting how pony orphanages would work
3- More Marble and Limestone Pie.
Maybe their farm is in dire straights and they need to come up with a plan to save it. Marble even figures marrying a rich pony might help and agrees to a choosing stone ceremony.
4- Gizmunks.
Always a fav of G1. These 2 tech oddballs were thwarted by Suprise and Danny's shenanigans. A gen 5 reboot would involve alchemy without the thought of consequence. And Trixie will have to use her illusions with Pinkie to stop them.
5- Seaponies
nuff said.
6- Catrina (sphinx) attacks.
Catrina is released from her tomb prison in Egypt (equestria version) and the Saddle Arabians summon the mane 6 to help stop her. (2 part) Twist, it wasnt Starswirl that sealed her.... it was Discord.
7- Travel to Zebreca.
Rarity and Zecora need to get Zecora to her home in time to an important celebration.
8 Stallions great escape.
Mac, Bulk Biceps, and Fancy Pants awake to find themselves ponynapped to Gelding Grotto. And they need to escape from the Amazon ponies that enslave males to serve them.