BLM's damage ceiling used to be locked behind procs in 2.x anyway, now it's locked behind really getting screwed with movement and standing there casting Fire IV which quite clearly is not working.

Besides, most classes have some kind of damage RNG to them (bloodletter, chakra stacks, Ruin IV procs, etc) and this would be no different. It's already fairly proc based with firestarter for movement and thundercloud, this would just make those more useful and more prevalent.