Here are a couple small features I'd like to see.
Multiple Regions or a big open-world region similar to BotW.
Soaring from ORAS was cool, but imagine how it would feel in a seamless open world, imagine taking to the skies riding on the back of your favorite flying pokemon.
Hostile / Friendly Rival option, basically ask us which kind of Rival we'd like to have at the beginning. Give everyone a choice, I know some people like hostile rivals like myself, others prefer friendly.. Let's have them meet midway.