The issue with brake lights is they are binary on/off. It would likely be better if the brightness would vary by how hard the braking is. Like getting brighter and brighter and then rapidly flashing.
Every car would have to have the same brightness for their brake lights for this to work well. At night, cars in the US have their brake lights partially illuminated as running lights. On some cars these are so bright that it looks like they're actively braking.
Brightness would be hard to discern in the sun. Cars have center stop light strip, it would be cool if amount of illuminated segments would be proportional to deceleration. Probably not legal though.
