I'd have thought the key was in always having a point at which the aircraft should be at a certain speed.
Doesn't work! It all depends on the wind. In a 45 kt headwind, you will be airborne very quickly. In a 10 kt tailwind, you would go as far as the performance would allow before hitting that point. So which applies on the day? I don't want to be looking for marker boards or things painted on the runway, I want to be monitoring instruments, and I barely have time to glance outside.
The old way works: set (correct) power, release brakes and away you go. There is so much performance margin built in to the take-off calculation that it can't go wrong. However, you cannot protect from idiots. If they can mess up the above, they most certainly can just as easily mess up assessing speed at the right place. In addition, different types require totally different performance measuring points- a heavy 747 take-off doesn't compare to a light 737 or Q400 take-off, so what are we then into? Look for a purple/green/yellow board as appropriate? How do you account for aircraft weight?
Solutions for aviation problems from non-pilots are always insufficiently thought through.