https://www.polygon.com/2018/9/12/17850280/pokemon-go-pokestop-nomination-beta

The ability to nominate local landmarks as PokéStops has long been coveted by Pokémon Go players.

Niantic announced that it plans to implement PokéStop nomination and that the first wave of beta testing would roll out soon. It will be limited to trainers in Brazil and South Korea, and only Level 40 trainers who are over 18.