Interesting concept, but I see a few practical problems in all but casual bike use.
In cyclocross or mtb applications, think of all the nooks and krannies on your current bike that don't quite get clean, imagine that thing on a muddy ride... it would be packed full of dirt and weigh much more.
On a road bike, think of the aerodynamic turbulence that would make. While lighter, it would most likely still be slower than an equivalent solid framed bike, just because of the extra drag created from the turbulent air created by those tubes.
