Cool, as I was reading this, was thinking in same line. Those magnets when trying to be pulled vertically will be extremely strong. Easily holding 60lbs+ with just single magnet couple of stacked quarter size. However, when you twist out of way (as in moving to side), the force decreases drastically. With proper pedal, I can see how this can be put into SPD format as well. It looks like to me the part where the shoe and pedal mate is to prevent accidental slipping to side where magnet will lose it's power. Instead of making it in single position, if they can make it in some section (say being able to move 1/2 inch on all 4 direction, it might be possible to accommodate rather wide range of motion while being able to held up.
The only concern I would really have with this would be... what kind of health impact does it have when you have such a strong magnet right on your foot for hours?