Has it occurred to you guys that there must be a reason why they did not directly announce that costumes carry over, unlike everything else that they have already confirmed to transfer, such as registered accessories?
Look, folks, I find no joy in saying this, but it's a NEW GRAPHICS ENGINE, in basically a BRAND NEW GAME, and a lot is not carrying over. Rebuilding an entire character with more polygons and entirely different graphical engine means the method by which the character moves, costumes are affixed, and the designs are implemented are different, which means that every costume has to be rebuilt from the ground up. In other words, every costume remade from scratch.
To understand this better, you need a firm understanding of character framework. In many old systems, the actual structure of the body was replaced with the costume, because it would've been way too many polygons and data to place actual armor on top of the character. Instead, your chest is replaced, the tone is matched on a Chroma wheel, and your actual chest is missing. The actual skeleton is swapped. Graphics engines do a lot to cheat in order to run on old computers and make it run faster.
There's absolutely a reason why they didn't say "all costumes and accessories will carry over".
My brother is a video game graphics designer with a lot of experience in the systems they used, as well as a PSO2NA player. When asked if the costumes will carry over, he laughed and said, "no, no absolutely not, otherwise it'd be another episode, it's inhumane to think they'd have to do all that work all over again."
I love my costume, but if it means the devs focus on the content, I'm willing to start with a new costume. Besides, how many hundreds of years in the future will this be? We can't even go 10 years without identifying a difference in fashion. 60s fashion versus 70s fashion versus 80s fashion versus 90s fashion.
It's okay for us to just be okay that they're starting new. I love this game and I am not bothered by this.
I mean that argument really only works for full on costumes and not things like outerwear. And they did say that registered things with accounts would transfer. Which at the very least means it's plausible for things like accessories and base/inner will transfer. They could also be vague because they haven't nailed down how much they want to carry over yet. It could also be a case of rights. Maybe they can't get the rights for certain collabs anymore.
We really don't know. Even if it was as complex as you're trying to make it out to be I can't imagine why they wouldn't be able to add a "legacy" setup where the looks of things actually carry over but they don't get overhauled to the nice newness that the NGS stuff is. Plenty of games have legacy setups.