Honestly, I expected a nerf like this to come sooner than later. Body and Soul is pretty strong in PvE, but no where near overpowered. Considering the new 4-piece bonus for the Priest healing PvP set, however, which allows the priest 4 seconds of snare immunity, the combination of that bonus and Body and Soul is unquestionably strong. Holy Priests may not have a substantial representation in arenas, but Holy has always been a very strong RBG spec.
I think a 40% increase in movement speed would be a decent compromise, but I would hate to see this nerf go live as is.