If finishers were to to cost only CP's and haste was no longer a factor in energy regeneration it would make it ALOT easier to prevent the scaling problems we see in rogues later in expansions while simultaneously bringing the class resource system in line with current melee with the exception of warriors. Other abilities could then be balanced with a more spammy state and make us feel more "active" in our combat rotations whether pvp or pve.
As Sin, I notice that in instances where I have 5 Cp's on a target and rupture and SND are already up I "feel" like envenom is huge waste of resources because of the double dipping for the pathetic damage it does. At 35 energy AND 5 cp's this has to be the most ridiculously expensive offensive attack in the game. It makes no sense what so ever to have to spend energy to gain CP's then to have to turn around and spend energy to use them as well.
Edit: This would also bring about what I believe to be the ideal role of a rogue in combat. That role should have always have been that of the quick striker. We get in and drop as much damage as possible as quickly as possible to take down the target. The longer we are out of stealth the more vulnerable we should become. With this in mind, the added burst would certainly offset our loss of control and instill fear in our targets once again.