Nobody has addressed this, but during the E3 2017 spotlight (this is speculative) Pokemon CEO Tsunekazu Ishihara looked emotionally depressed when he announced that a Pokemon Switch game was in development. I interpret this as an attempt to rectify the extremely negative feedback of the Pokemon Direct just before E3. It's as if, instantly he decided to start working on a new Pokemon game for the Switch based on the vociferous outcry as it left both him and the fans in disappointment. So, I very much doubt that this Pokemon game has been in development before the Switch was released.
Either
a) Game Freak are going to push for a 2018 release and work hard on this new game (maybe reuse some HD assets from mobile?)
b) No 2018 release at all. Misconception.