It seems to me like the capabilities of the Twiddler could be greatly expanded with some kind of feedback mechanism. A screen is a bit much and over complicates things, a speaker is disruptive. But a small vibration motor like that found in a cell phone would be really awesome. You can make a million different vibrations to tell you different things.
The biggest use case I see for this is untethered chording mode (which is awesome). Vibration could be used to confirm you are indeed in untethered mode (right now it's kind of a shot in the dark and the LED is not always reliable). Additionally you could use vibration to navigate between multiple untethered storage files (1-10 vibrations, etc.).
This and many other useful things could be done with a simple vibration motor.