It could be tough to make universal - there's a big variety in tail lights used and driving mechanisms (not many relay drive ones left, but can you imagine the thrashing

) . Depending on bulb type, you could also run into switching issues if you were using particularly high intensity lights, different types will put in different limitations, so a "universal" drop in system could be pretty low performance compared to, for example, an all LED light car.
I think the bigger block could be the camera technology, actually.... because of framerate. Unless you're going to PWM the lights to encode the data as effectively analog, your 60fps camera would struggle to get anything more than 30bps datarate. If you could shrink the resolution to get more framerate you can probably do better, but you're still talking a few hundred frames per second, tops, so your datarate is still low enough that a unique identifier for the vehicle and overhead for a small ID packet being transmit could take multiple seconds. There's also the issue that if your data is being transmit this slowly, it will manifest as flicker which could be distracting/unsafe on the road. If you can get the frequency to a few hundred Hertz you can avoid it, but then your camera has to be specialized to be able to pick it up.
The typical optical data link is a set frequency pulse modulated with the data, basically the same idea as a radio link, and I don't think cameras will be able to manage that. If you're going to try to develop a device to find such a signal, you need to make sure you can actually modulate your lights at the required speed, and you probably want to be looking at camera cores that offer 240x180 or lower resolution modes at a few hundred fps.