Doug: it is not for nothing that De la Cierva invented flapping hinges in order to solve the dissymmetry of lift, preventing the blades from breaking.
Concerning VAWT I think there is some possibility for giant installations (about 1000 meters diameter and more) lengthening the rotation time, such like the device on the sketch below:
The too low density in a farm of HAWT is a crucial problem. If giant VAWT are implementable the density issue can be solved, at least for offshore wind turbines: a single VAWT becomes like a farm of HAWT whose units are scattered over too large areas.