How to make fansub form with xthreads?

[ZiNgA BuRgA]

I suggest you examine the Lyrics forum and Books Review System more carefully as you'll probably find them to be quite different.
If I understand you correctly that is.

Forums aren't designed for collaborative editing, and XThreads won't magically add that function.
Comments is doable, but the other features probably not, and there's no nice methodology for a timeline.