Hey it's still not out of the realm of possibility they re-add it in an update. They did say more course parts were coming, and maybe they needed time to get the licensing sorted out for the 3rd party costumes. Or they're trying to implement them in 3/World too with unique sprites, which would take longer to make.
man id LOVE costumes to be back!!! but im just not expecting them anymore since they werent in the base game
they were really charming its sad to see them just be gone for some reason