Really? Do you have trouble distinguishing the left/right turn signals that are shaped as arrows from a distance? I've never once had problems with that and, as far as I know, none of my friends have either.
The thing is, I DO NOT NEED to distinguish that it's a left arrow, because nothing else can light up left to main R-Y-G traffic lights. Now imagine that you have a fourth traffic light below the R-Y-G lights, it may light up as a left arrow, or as a right arrow, in the same place. I would have trouble in that situation, distinguishing between the two arrows.
BTW I live in Russia and weather is poor here most of the year, and most traffic lights are made of arrays of rather big LEDs which are brighter and blurrier than older lamp-based traffic lights but make the shapes harder to distinguish. I guess in the US it's better.
In any case I don't mean to suggest that traffic lights should be only different shapes but rather that shapes be used in combination with colors. I feel like it would be an easy transition to make as the shapes would be a supplement to the existing system and thus traffic signals can be changed gradually.
The article's idea of making the green light blue would certainly help me but it does nothing for people who are completely colorblind and present the problem of transitioning a standard.