I used to ride a motorcycle every day from the suburbs to Chicago's loop (until a crash on the way to work. heh) and I'm not sure that I'd want something like this. As binary as it initially seems, there's actually a lot more contextual information to it than you'd think. The swerviness, the length of the brake, how straight their car's going, how often they do it, head position, how in depth their conversations seem to be, etc. Like a lot of riders out there, I started playing mini games to try and figure out what the drivers were doing to help with determining risk. For me, imagining the physical position of their driving limbs, as weird as that may sound, was the most help. Thinking the problem in those terms helped out and really pushed the idea that if their foot is hovering over the brake, then a lot of caution is needed. I don't do this as much in a car, and I doubt many drivers do this, or anything close to it.
I think that if something like this was implemented, then a lot of people would use it as a crutch and make poor decisions based on implied safety eg, "His light didn't blink three times, so I didn't think to stop." That, and a lot of new cars, for some stupid reason, seem to want to obfuscate the significance of brake lights by just having them be brighter versions of on-by-default lights anyway or similar.
There definitely is something along those lines that'd be helpful, but I think it might have to be all or nothing there. Flooding phone frequencies with white noise might work, though ;)
