That is such a cool idea. I'm trying to figure the ideal implementation - a building with a lot of stone, concrete, and steel - and also pre-wired for cable. Small n.

Years ago, I had to temporarily extend a network between floors in an old building south of London. Stone walls and foot-thick concrete floors, with no useful telecom shafts between. The landlord didn't want us drilling holes ("Really, your next tenant will love it!") or using the stairwell. We finally just dropped a cable out one window and into the next. Ugly, but functional. <sigh> Gotta do what you gotta do.

As for the passivity - I suspect it's in that coax is far better at holding a signal, and can induce enough followup signal at the other end. But I'm not an EE.

-jk