Hajime Tabata, the director of Final Fantasy XV has revealed in an interview with Italian website, Game Legends at Let's Play 2017 that a multiplayer beta for Final Fantasy XV will happen for the Comrades expansion. Keep in mind PlayStation Plus and Xbox Live Gold are required for the multiplayer.
But that's not all. Tabata also teased a story expansion for Ardyn. However it's not clear if it would be a DLC episode like Episode Gladio or just new cutscenes in the main game.
Source: Game Legends