If it was only just Phantasy Star-related items (such as character outfits, cameos from different games, or other Sega-related properties) I could imagine this probably would have been achieved, or at least would be done. But in the Global version we don't have the presence of Cougar NX therefore that I don't know if there are additional complications regarding Sega's own properties that might also contribute not to updating everything they could within reason.
I can envision that probably out there we will still see somebody wearing those old collaboration items even when they are not rigged up to the very same criteria as new cosmetics at an identical way and that there surely would have been outrage when it was made obsolete or unusable. Collabs who have experienced their cosmetics removed still have their assets exist on the game so those will probably still be accessible for jp players.
Only improvements we'll probably see is the brand new engine improving shadows, reflections, colors, particle effects and projecting them from the drapes. You may have a look how just implementing better shadows and colours can improve older equipment by assessing ReShade screenshots. Collabs that have experienced their makeup removed nevertheless have their resources exist on the sport so those will probably still be available for jp players. Only improvements we'll probably see is the new engine enhancing shadows, shadows, colors, particle effects and casting them against the drapes. You can take a look how exactly applying better shadows and colors can enhance older equipment by checking ReShade screenshots.