You mean like one of those
FPS Feedback vests? I guess feeling like you got shot would be great motivation to not miss...
Back on topic, however, closest I've heard of for "wearable" FRC tech were the old pseudo-HUD glasses that seem to have mostly fallen out of favor. The concept was cool enough though; stick a LED on a pair of safety glasses or a clip and it turns green when you're on target, red of you're not.