They won't take away rogue passive damage. Runs the risk of rogues becoming too bursty which will then get us nerfed faster than a red headed step child gets a beating. We had burst back in the day and ever since then the entire game has been changed to prevent something similar from happening and more and more of our damage goes into passives.
Think about the consequences of having more damage moved out from auto attack damage and into our abilities. Sub rogues are arguable one of the highest burst on demand on a short CD specs in the game. Granted it'd be fun to run around killing people in a shadow dance but realistically the tears of rage from the rest of the community will drown the entire rogue class out of the game. Hell even combat would cause some rage with adrenaline rush becoming hugely op if most of our damage was in specials.
If pvp wasn't a factor in this game I'd agree with you 100% and think that special attacks should be flashy and flavorful. But, pvp balance is a slap in the face to fun.