I've surveyed several ferro cement yachts over the years and not a single one didn't have a rusting steel armature. Even well protected wire cages get a ding or nick during the pour and this is the beginning of the rust process.

I've never heard of the "thin sheet" described above and don't understand it's potential from an engineering stand point, but this doesn't mean it wasn't tried. Most don't realize how flexible concrete really is, nor the actual role of the steel reinforcement within it.