Edit:As best the machines can tell me, it looks like there have been more changes to this costume than in past costume updates, with even a new concept. However, the colors are the same, and they tried to keep a balance so that it apparently still looks like Miku.
I guess we'll have to see what that actually means when the new design is shown off. Not surprised that they're making bigger changes, since she's getting a radical fundamental change, too. But I'm sure they've tried to keep what they feel are the most important/iconic aspects of her appearance intact.
I wonder if they are going to base part of Miku NT off the Yamaha Reface DX. (I own that keyboard and it's amazing.) It would be cool though, but again, we're all not sure yet.Going to go ahead and add @Exemplar's finding about the new Miku NT character design here:
Like I mentioned over there,
Wat mentions something like that the new design concept takes some inspiration from a voice "wave," so it has a streamlined look, and also is intended to be feminine/clean/pretty. Symbols from the DX (Yamaha DX) are still present, but seem to have been reimagined.
Wat mentions that it's been 13 years since he asked KEI to incorporate DX symbols in Miku's design. It was hard to change some of those things for V3/4. For NT, some of these symbols are difficult to touch, but he feels they've taken things in a "Crypton" direction.
Wat thinks they'll be able to reveal the new design later this month.
I'm really not sure what these mean, but he seems to be talking about user interaction/feedback (and costume design?) in Project Sekai and seems to say that NT may take some cues from Sekai somehow. The translation's not clear enough for me to feel very confident at all about interpreting these, though.