Compare the risk involved in being a Taxi driver with other jobs. Even as it stands (no back seat eject option) driving a taxi is arguably safer than tending bar, delivering pizza, delivering crates, factory work, playing a medic or doctor. Most every other job involves you being in the same accessible space as your customer. This puts you at risk. Not so much with taxis as I have gathered.
Beyond that look at the power a character gives a taxi driver. They get in the back of a cab and they are largely at the whim of that taxi driver. They get locked in. They can't really DO anything to my knowledge until the doors are unlocked. Except yell and feed the driver more chy.
All this would do is allow a weak character to override a more powerful character. You can still create RP. If a character won't pay, your character gets in their face. Your character threatens, beats and whatever else. But in a way that puts them at some level of risk. Maybe you get your ass kicked and now you avoid driving for them ever again. Maybe you kick their ass and now they have a way to get revenge. I don't see how removing most all risk from the driver increases RP...
Again, this is all based on my very limited experience with taxis and other vehicles.