For the 10+ years I have been driving (Eek! Has it really been that long?!), people who do not use their turn signals have been a constant point of irritation to me. Clearly, directionals became a required feature on all vehicles because they make driving safer for all of us. Just think, if everyone used their blinkers, there would be fewer instances of unexpectedly getting cut off on the freeway by non-users and you could confidently make that left turn without wondering if oncoming traffic is going straight or turning.
For these reasons, among others, if I reigned supreme, I would install a new standard feature on all vehicles that actually prevents you from turning or merging unless your turn signal is activated. If we can design cars that stop (safety feature!) and parallel park (convenience feature!) themselves, I think we can do this for both safety and convenience.