Gosh, this looks so complicated. On the 1 hand, kudos for PSO2 Meseta maintaining the game intact so that there will not be a riot over changes people don't like. However on the other hand, since they are remaking base PSO2 visuals anyhow, I wish they'd only go 100% and synchronize personality versions completely. Giving old players some free fashion items and unlocks would be enough to bribe everyone to take the new system.
Synchronizing 100% character models does not sound simple. The dilemma is that the older outfits and coating wear are modeled to fit the older pso2 body. That's unlikely to happen. Well, I mean that I'd be willing to shed a certain proportion of these cosmetics to keep things intact around versions. As long as there's a steady feed of cool new stuff to replace it, I do not mind. I constantly rotate out my old looks anyhow. As long as the character models translate 1:1 it will still feel just like mine.
I would envision a large complication to this involves a lot of the makeup from the Japanese side of things that were exclusive to collaborations, promotional events, and events that no longer exist. The example I can think of is that the Monster Hunter Frontier Z collaboration where I could imagine the clothing and weapons could definitely be provided a visual update alongside everything else but that I do not exactly know how the licensing or how the lawful side of this cooperation functions where I'd wish it was as simple as Sega going through and upgrading the resources but I don't understand about just how much Capcom is involved in this procedure.
The same is applicable to collaborations such as the Final Fantasy XIV collaboration with Odin (which exists as far as I know) where I don't know just how much of Square Enix is involved that for Sega to be able to upgrade assets there. When it was only just Phantasy Star-related items (such as character outfits, cameos from different games, or alternative Sega-related possessions ) I could envision this likely would have been done, or would be done. But in the worldwide variant we already don't have the presence of Cougar NX so I do not exactly know if there are other complications regarding Sega's own properties which may also contribute to not updating everything they can within reason.
I can envision that likely out there we'll still see someone wearing those older collaboration things even if they are not rigged up cheap meseta pso2 to the same criteria as fresh makeup in a similar way and that there would have been outrage if it had been made obsolete or unusable. Collabs who've experienced their makeup removed still have their resources exist on the game so those will probably still be accessible for jp players.