Persona 5 launches on PS3 and PS4 on April 4th of this year and there will be a plethora of costume DLC and classic Personas that will be available post launch as well. A lot of these costumes are based off of previous Persona games and the Shin Megami Tensei series. A lot of these costumes come with new background music which can be played in dungeons as well. For instance, equipping the Persona 3 costume set will change the background music in dungeons to "Mass Destruction". Also, Morgana dressed as Aigis is adorable.
Here is the list of planned DLC, release dates and prices from the official Persona 5 English website.
Persona 3 Costume and BGM special set
Persona 4 Costume and BGM special set
Orpheus and Orpheus Picaro set
Thanatos and Thanatos Picaro set
Izanagi and Izanagi Picaro set
Shin Megami Tensei: Persona Costume and BGM set
Persona 2 Costume and BGM set
Kaguya and Kaguya Picaro set
Persona 5 Swimsuit set
Shin Megami Tensei IV Costume and BGM set
Persona 4: Dancing All Night Costume and BGM set
Catherine Costume and BGM set
Devil Summoner Raidou Kuzunoha Costume and BGM set
You can check out the DLC trailer for the Persona 3 costume set below, courtesy of Persona Central.