Currently the shuttle script is set to start playing backwards if J is pressed when playing forward, or to start playing forwards of L is pressed when playing backwards, regardless of the speed of playback.
In Adobe Audition, the same keys are used for shuttling, however if the speed of playing is greater than 1x, then pressing the opposite play direction key first decreases the speed in the direction it is playing until the speed reaches 1x and only then does the direction reverse.
This is much closer to how a real shuttle controller works, and hence would be a very useful improvement to the shuttle script.