During last night's Nintendo Direct, it was announced that when Dragon Quest XI: Echoes of an Elusive Age comes to Switch this autumn, it will arrive as a Definitive Edition of the game. This new version will feature new content, and perhaps most notably, new missions for each character in the main party where they get to briefly be the protagonist of the story.
Dragon Quest XI is already available on PS4 and PC, but it's not yet decided if those players will get the chance to experience this new content for the game.
— Takashi Mochizuki (@mochi_wsj) February 14, 2019
Takashi Mochizuki, tech reporter at The Wall Street Journal asked a Square Enix representative if the content would be coming to other versions of the game, either as a free update or paid DLC, but Square Enix simply stated they were “undecided.”
So, for now Switch is the only place that can guarantee you this new content. We will update if we learn anything further about this content getting brought to other platforms.