007, interesting idea. Unfortunately, I am not sure that it would work. If I have understood your picture correctly, wouldn't you have to remove the saddle to adjust the height?

Also, you would add substantial weight by having a bolt run the whole length of the seat post. By "substantial weight" I mean in proportion to the weight of the seatpost and the clamp. Obviously, the bolt would be small in comparison to the total weight of the bike, but it would likely be as much as 10 times the weight of a seatpost clamp.

Nevertheless, interesting idea.

Cheers,
Jamie