I would love to see a remake of Envenom to make it more rewarding.
Something along the lines of lowering poison proc rate outside of Envenom and increase the proc rate during in order to make for a more active rotation. I feel that the difference between keeping Envenom up or not is too small as it is (15% extra proc rate). Low uptime should really hurt while managing high uptime should feel rewarding.
Further on, the spec does have a really boring cooldown in the form of Vendetta. I would like to see a cooldown that actually interact with poisons, the main concept of Assassination.