The goal wasn't to be seen in full sun... for that, your outstretched arm should be quite sufficient (provided motorists have a clue...).

The goal was to provide something for signaling at night. A light is a nice idea... but the arrow scheme they chose would require a cyclist to signal in an unusual manner... and worse yet, signal with one set of arm movements during the day, and a different set of arm movements at night.

The best solution is just a single round spot of light on the gloves.... or as others pointed out, a leg light on your wrist. Frankly, I would prefer something that didn't require me to buy their gloves at all... over the years I have learned that I prefer a few certain styles of gloves for long term hand comfort... and the last thing I would want would be to HAVE to wear a glove that perhaps I found uncomfortable... just for the signal aspect.