A Dark-Type Gym, preferably 7th or 8th in the league.
A difficulty option accessible from the start of the game.
A Battle Frontier; the PWT could be located within it.
An underground and base system, similar to the one in DPP.
The game takes place simultaneously with X & Y. The post-game allows you to travel to Kalos, and triggers the beginning of a storyline similar to X & Y, but incorporating Zygarde, effectively acting as a "Pokémon Z."
The return of Pokémon following you.
The return of character customization.
A Key Item that you can teach four HMs to ("HM Doll").
A gripping, thought-provoking story with complex characters and lore.
I want an NPC to appear on the boxart, along with the mascot. Who the NPC would be would be heavily dependent on what the plot entails, but I think it would be nice to have an NPC on the boxart for once along with the mascot (even if the mascot wasn't a legendary). (For example, maybe a special wrap-around boxart with the mascot and one of the protagonists on the front, and the villain and another appropriate Pokémon on the back, as if they're ready to face off against each other.)
- Going off of this, HGSS effectively had two boxarts because the game came packaged with the PokéWalker device. If Sun & Moon were to contain some sort of external device (maybe the Pokémon Go watch-like thing, since apparently Go is meant to connect to the main series in some way?), the outermost box could have a "special" boxart like the ones I've described, while the boxart for the game itself would have a more standard, Pokémon-only design.
There are other things that I think would be fun little bonuses, but I think this is a good starting point for things I really,
really want (read: think should be included) in these games.