Manly scott's transonic trussed based wing video triggered a wave of interest in toroidal propellers.

The thing is, ring wings have been around the rcgroups & gizmodos for 20 years but the message didn't propagate at all until a Manly scott made a vijeo. 

They're being emphasized just as quad copter propellers, probably because quad copters sell more ads than ventilation fans.  In reality, the extra weight of the joiners doesn't help quad copters.  The mane benefit is in making them quieter.  They could be a good way to make ventilation fans.  A wall of fans which would have been too noisy might be practical.