Has anyone considered doing or done a 4- or 5-point harness for their vehicles to replace the standard seatbelt system? I suspect there may be some issues with the safety part of the car's electronics and may even be illegal in some jurisdictions to mess with the OEM belts.

 

4 point is a bad idea. You can submarine under. I have seen many bad out outcomes at tracks throughout the country back when 4 point was popular before people were educated on the issue.