The same is applicable to collaborations such as the Final Fantasy XIV collaboration with Odin (which still exists as far as I know) where I don't understand just how much of Square Enix is involved that for Sega to be able to update assets there. When it was purely just Phantasy Star-related things (like character outfits, cameos from other games, or alternative Sega-related properties) I could envision this likely would have been achieved, or would be carried out. But in the worldwide version we don't have the presence of Cougar NX so I don't exactly know if there are additional complications seeing Sega's properties that might also contribute not to upgrading everything they can within reason.
I can imagine that probably out there we'll still see somebody wearing those old collaboration things even when they are not awakened to the very same standards as new makeup in a similar way and that there definitely would have been outrage when it was made obsolete or unusable. Collabs that have had their cosmetics eliminated still have their resources exist on the game so people will likely still be available for jp players.
Only improvements we will probably see is the new engine enhancing shadows, reflections, colors, particle effects and projecting them against the outfits. You may have a look how just applying better shadows and colors can enhance old equipment by assessing ReShade screenshots. Collabs that have had their makeup removed still have their resources exist on the sport so those will likely still be accessible for jp players. Only improvements we will likely see is the brand new engine enhancing shadows, shadows, colors, particle effects and casting them from the drapes. You may have a look how exactly implementing better shadows and colours can improve older equipment by checking ReShade screenshots.