I agree, this would be a very safety-conscious improvement. Typically, I pride myself on turning my signals off Immediately after making the manuver for fear of misleading others (unlike some of the folks I sometimes ride with). But just this morning on the way into work while stopped at a light, I realized my right signal indicator was on. I had to think long and hard to even remember the last time I had made a right turn or lane change. Thankfully nothing bad happened, but the signal would not have been left on if they were automatic turn off.
Ride safe!