Don't get me wrong but I feel it would be a lack of professionalism not to have the whole song by the time the movie is released, and to be featured in the movie it should've been finished by now since the movie's premiere is next week.
Pessimism is unfortunately, the mood I'm having about this.
I think the song is finished, and was recorded a long time ago. In the Buddha trailer the clip of the song featured real drums, piano and vocals (normally Yoshiki leaves recording drums until last, I still think he hasn't finished them on Born to be free).
I just think that, knowing Yoshiki and X Japan, they probably wont have the entire song involved in the movie, but probably just a clip, as he did with VUK-R at the end of REPO.