It feels like the show brought a lot of character arcs to a close, or near to a close, this season:
Twilight’s is pretty obvious: She’s gone from antisocial loner, to slowly coming to understand how to relate to others, to de facto leader of the Mane Six, to member of Equestria’s ruling class. She has an obvious next arc, though, which is learning to balance her personal friendships with her duties to all of Equestria, as well as learning what those duties are and how to express them.
Fluttershy has slowly learned that she does have a valuable skill that can serve her in a confrontation, namely her ability to use body language, tone of voice, and careful observation of the needs and wants of her opponent to resolve the conflict nonviolently. She’s gone from “only able to use it on animals” to “able to use it in a crisis” to “able to use it on Discord.” Her next arc is not obvious.
Rainbow Dash has gone from arrogant, brash, and heedless of the consequences (she kicked a dragon in the face, and Fluttershy had to calm him down!), to being able to recognize the potential consequences her actions may cause to befall herself and others, and making an effort to minimize them. She’s also joined the Wonderbolts, apparently? Ish? That episode ended very abruptly. Her next arc is not obvious.
Rarity doesn’t have an arc so much as a negotiation, balancing her desire for fame and social status with her love for her friends. She’s several times had to waver between these in an effort to find an appropriate balance. There’s no particular reason she couldn’t keep struggling with it, but at the same time it’s feeling a little played out (which is probably why there were no Rarity-centric episodes in Season 3). Her next arc is not obvious.
Pinkie Pie’s finally learned some restraint. She went from needing to learn that her friends love *her*, not just her parties, to having to adapt to the notion that different people have different relational styles and boundaries, to being confronted with questions of just who the “real” Pinkie Pie is, and she’s finally starting to grow up a little. Again, it’s hard to see what her next arc is.