I don't think anyone's mentioned this, but I just realized something else after browsing Tumblr on my phone:
That's making me wonder if the outfits are based on the personas themselves, and if so, if we might already have clues for what Ryuji's, Anzu's, and Morganna's might look like. The black marks on the mask look like they could be a stylized way of representing the persona's fiery eyes.
The shirts between The Phantom and his persona are actually really similar - they're not 1:1, but they seem like they could be made of a similar material, and the white dots on The Phantom's shirt correspond pretty well to the hole's for the persona's red cords. That, and it'd seem like it'd be easy to stuff a cravat into his get-up if you undid the collar.
That's making me wonder if the outfits are based on the personas themselves, and if so, if we might already have clues for what Ryuji's, Anzu's, and Morganna's might look like. The black marks on the mask look like they could be a stylized way of representing the persona's fiery eyes.