Several questions: Would this camera be for use after an incident, or while it is occuring?
If during an incident, how would you ensure that the camera is pointed in the appropriate direction, unless you plan some sort of 360 degree setup? Second, how to trigger it (or do you just run it continuously?
For afterwards, I generally have my cell phone (with it's reasonable camera) with me, and given 20-30 seconds prep time, I can take photos of an accident scene, etc., unless I am incapacitated or the phone is broken. Whether I can get it into play quickly enough to capture a license plate number, etc., would depend on the specific situation.
I do know of a couple folks with velomobiles who have mounted vid cameras front and rear. Some of their vids showing peoples' reactions to the VMs are pretty hilarious.
BTW,
RAM Mounts makes almost any sort of mount you can think of. Want to take your laptop on your bike?