Unfortunately I do think they would still lead with there head. A text book tackle involves putting your head in front of the body of the ball carrier. If you go low, the posibility of getting a knee to the head is very real. While I agree with the theory that helmets and bigger pads have led to more violant collisions, I don't think taking the helmet away would decrease head injuries.
I agree with you that protecting the qb's from the free head shots they were taking a few years back is a necessary move.