This new patent shows Sony is working on Fresnel Lens technology

Nikon currently has two 500mm and 300mm Fresnel lenses in their range. This technology allows to make smaller and lighter lenses compared to traditional lens designs:

The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet.

One of the downsides of Fresnel lenses are the Flare artifacts. But a new Sony patent proves that they are ready to launch such lenses with a new tech that can suppress the flare issue:

The present invention has been made in the light of the actual situation described above, and one of objects thereof is to provide a Fresnel lens and a method of manufacturing the Fresnel lens which can suppress a flare which is generated in an image visually recognized through the Fresnel lens so as to extend toward a center of a lens.

Finally we might get closer to our dream to have both small FF cameras and small FF lenses?