End Plates
The shroud of a ducted fan acts as an endplate without putting any extra mass at the ends of the blades. That's why the clearance between the blade tips and shroud needs to be so small. The mass at the ends of the prop blades has to be minimized to control the centifugal forces. If too much mass were added at the tips the blade would not be able to stand the stresses and fly apart. Many props are already on the verge of doing that without the mass of end plates.
Planes like the Dust produce the required lift by a combination of high speed and low coefficients of lift. At low coefficients of lift the induced drag is already low so the opportunity to lower it is limited. It would take a very large end plate to lower the induced drag appreciably and that would make much more parasitic drag than the induced drag reduction. If end plates resulted in net drag reduction you would see them on airliners for fuel efficiency and range advantages and on sailplanes for L/D advantages.