Good idea- let LS die, and make wrath just proc crushing as well as finish crushing's cooldown. Make crushing stack, or, make it so if you use crushing on someone who already has the dot- it instead does all its damage at once.
Suddenly- burst damage.
Sounds like a good idea for madness, although I don't think they need to change lightning strike as the filler for the lightning tree. Just make it more effective. It needs a damage boost.