If you can trust her dancers singing in her stories, then it's for Haircut.
When she posted two days ago in her FC blog, that she's preparing this special PV, she talked about costumes, not outfits.
Reminds me more of Shake It Up PV than Butterfly.
Considering the lyrics of Haircut, she may address her changing and progressing over time over the span of her career.
With the post she says she's not done filming yet (it's already the middle of the night in Japan).
The dress or whatever she is wearing there is Versace.