Oh man, have I been waiting for a thread like this for a while. So this year, the programming team for 540 used wearables for the drive team itself. We used the Vuzix m100 smart glasses which run on Android as a substitute for the driver station's dashboard. Essentially, information such as whether we had a ball in the intake or if we were aligned to shoot were sent to the Vuzix smart glasses and were displayed as lights in the Android app we developed. This implementation was AFAIK legal because it used a wired connection (port forward from laptop to smart glasses using ADB interface through a USB cable) and the secondary driver didn't put it on until after autonomous ended (took him like one whole second). I'm super excited to have led this project and hopefully our team will use such technology in future years to provide intuitive data to the drivers! Don't hesitate to PM me about how the smart glasses were implemented because I'd love to explain it and hopefully increase the usage of cool new technology in FRC
EDIT: For anyone wondering what this looked like to the driver, imagine holding your phone in landscape mode almost an arms length away in the top right of your FOV. It was very natural for the secondary driver to glance up to check if we were aligned to shoot or if we successfully picked up a ball into the intake