I have to ask ... why?
Do you think it would be too powerful? Or not powerful enough? Remember this particular change shouldn't affect anyone that already prefers Full Auto or Sneak Attack (lets face, everyone apart from support professions and Agents ...), as the shared cooldown means you shouldn't ever be ASing.
So making it castable effectively nerfs the aforementioned support professions. That's actually ok - support professions are supposed to be getting easier to land nano-toolsets, which is a far bigger buff than this will be a downside.