I wonder.

If BRD stays at the same efficiency compared to other DPS without using this new song as it is now, and the new song helps us boost that DPS, then it's good.
If they make it so that BRD *has* to use this new song frequently to be as effective as they are today, it's a huge nerf and will make tons of BRDs switch classes.

I doubt any BRD picked up the class to stand around and deal with cast bars - that's what BLM is there for.