What a great idea.. I like it. Lets see re durability..My normal seatpost is 1 mm too big as it is difficult to put down. That idea would solve that. Plus lower weight.
http://www.pinkbike.com/news/orbea-digit-dropper-post-first-look-2015.html
http://www.pinkbike.com/news/orbea-digit-dropper-post-first-look-2015.html