Since a few others have started thinking of new story ideas for MLP with most of season 7 already revealed, I think I'll do the same. First, a link to my season 7 ideas since many could still be used for season 8:

Now for other ideas:
Princess Pants
Twilight is invited to Princess con at the huge request of many of the organizers (and all the other princesses being conveniently too busy to attend). It doesn't take long before she finds out why all the others found excuses not to come as she deals with things like "The Princess Experience" simulation being a rose-colored glasses look at what being a princess is. Things take an even worse turn when a fan war is going to break out between the different groups who each think their favorite princessis "Best Princess." Will Twilight be able to make it through Princess Con or will she have to put her trust in... Princess Quibblepants?

Me, Myself, and Discord
A little prank by Discord causes quite a bit of chaos around Ponyville. Fluttershy finds out, but rather than tell on him, she wants him to come clean. He refuses and Fluttershy wonders if he can live with himself after doing that to which Discord scoffs since he has never felt guilty about causing trouble before. Discord then creates a copy of himself to prove his point and watches as the other Discord goes around causing trouble. He soon starts to feel bad seeing all the trouble the other him is causing, but when his copy is having too much fun to stop, will Discord be able to stop himself?

Journey to the Center of Equestria
Spike wants to get Rarity a very special birthday gift, a gemstone more beautiful than any other. Starlight suggests asking Maude for help. They learn from her that there is such a gemstone deep underground where few ponies have ever gone. Spike goes with Maud to find it, but when the situation grows more perilous will the be able to get the gemstone and make it back out?

2 Griffins 1 Stone
Gilda's attempts at bringing friendship to Griffinstone have been met with mixed results since Pinkie Pie and Rainbow Dash visited. Some Griffins have become her friend, but others have been proving as stubborn and selfish as ever. In order to try and fix this, Gilda takes some advice from Pinkie to throw a party and with a Griffon Holiday that hasn't been celebrated in ages is coming up. Gilda gets everything set, but when she learns that a ceremonial stone is needed she has to hurry and retieve it from atop a mountain by foot alone. Despite this, Gabi goes too knowing how dangerous the climb is and wanting to help out. Will these two be able to get the stome and to get the party started?

Some Fiends Never Change
Chrysalis returns to the hive starving for love. She has been unsuccessful at getting love on her own and cannot even must up the strength to transform. Thorax is worried letting their former queen in might be a bad idea if this is a trick to take over again. Despite this, Thorax must continue to set a good example for the others about sharing love and friendship. But is Chrysalis really to be trusted or will Thorax's reign be short lived.

Left in the Dust
The Cutie Map calls Starlight and Fluttershy to the Wonderbolt Academy. There they find Lightning Dust is once more trying to get through the Wonderbolt Academy, but one thing is stopping her, she is unable to find anyone to fly with due to desire to always be the best and none of the other fliers able to keep up. With the test coming up will they be able to teach her to be a team player by having her be Fluttershy's Wing Pony or will Starlight have to rely on an old spell to help even things out?