I think that's a brilliant idea.
When I used to work as a taxi driver many years ago, the call went out as a code 13, if you could talk on the mike, or there was a hidden button on the steering wheel too.
The dispatcher could then hear the inside of the car, and they would put out a code 13 to the address and it was the other cabbies who would be there as soon as illegal speeding would get them there.

You are very correct to assume that the drivers will look out for their own.

And now, the technology must make it easy to have a similar function built into the app.