Interesting idea. I'm not sure if this is needed, though, because the current system follows the basic principle of "if you see blinking: watch out. If you don't see blinking: don't mind".

Bulbs don't fail that often, plus it would be a lot more complicated and take a lot of effort to watch out for certain blinking patters that could still tell us that a car would turn in a certain way if its bulbs are defunct. Much easier would be if a car driver with defunct bulbs would be notified in a certain way so that he can drive more carefully (which I think certain cars already do).

This thought of drivers being notified if a bulb is out needs to be looked at. I think most cars will blink at an accelerated rate if a bulb is indeed out it depends on the wiring I believe. Contrary to your comment that bulbs rarely fail I see an awful lot of dead bulbs on the road, road condition in my area may contribute to this. The thing is I don't think a lot of people are aware why their blinker is fast or they may not have even noticed the speed. Why not have something akin to the door ajar indicator on some vehicles only this displays a non functioning bulb's location when the key is turned?