The current shield a car gives you is 50%, so if you get hit by a BAR it'll only do 5 damage. I believe he is referring to how the car protects the players, an update could upgrade your shield to reduce 60% of damage, and then another to 75%.
This is a fantastic idea, as cars are quite weak, and are barely faster than a player. Doing this will encourage more players to do car missions, and I can see this becoming the new #1 job.
On that fact, players should have an option to purchase access to exclusive car mission NPC's, a similar concept to the Veteran Speedy Pizza, either by having a new "showcarmissions" command or using gralats to gain access. This offers a reward for willing players, and makes it easier to get money, much like veterans pizza.