It could totally happen. The armor would need to be made of the same "high impact " plastic that is used in paintball goggles. Then it would need to go through tons of testing and certifications. Then mass produced and packaged for the retailer to provide for the customer. So, if someone had deep enough pockets and wanted to spend THOUSANDS of dollars on it, then yes it could be done. And yes, it would be sooooo cool!
Like Phil, I am a veteran paintballer (26 years) and just go buy a new lens. First off you don't want to mess with the integrity of the lens, and most of them now are dual curved, so it would be a nightmare to tint it. Not to mention tint would maybe last for a couple dozen shots to it before it started to peel.