He sees the partly-resonant design as a competitor to hard-switched high ratio topologies – such as for 48V to 1V conversion, where on-time is so short that GaN switching transistors are being proposed.

His uses a tapped inductor, two mosfets and a diode to get the same ratio without extreme on-times, or nasty ratings for the components.

It is described in US Patent 7915874.

and also in this video where Cuk – describes the subtlety – sadly the video quality is not great. The image is taken from the video.