Square Enix has confirmed Nier Replicant's extra content via a new trailer.
In the video, below, we see an extra dungeons, extra costumes, the guest cast from Nier: Automata, and a look at an extra episode called Mermaid.
15 Nightmares – aka The World of Recycled Vessel – first released as DLC for the original 2010 action adventure. This is now included in the main, remastered game.