Can we not just buff LotV to the point that it becomes mandatory?
How does Blizzard expect to balance a talent that completely changes the spec playstyle like LotV will? I have a strong suspicion it'll either be bad, or so strong that you are forced to play with it anyway.
Trying to retain that playstyle is a mistake. It's going to be nigh impossible to keep it competitive without it just being inevitably better - and you're basically taking the shadow spec and making two versions of it that each have to be balanced because of how drastic of a change that one talent makes to the specs playstlye.