https://jp.motorsport.com/super-form...%82%82-943678/
According to jp.motorsport.com,
Akira Kurashita (JRP) says that there is a possibility that air restrictor might replace fuel restrictor in 2019.
If so, current overtake system doesn't work. So DRS might be introduced in 2019.
2018 technical regulations change is to test DRS in 2018.