I have very high opinions of where science and imaging technology will go. Can the diffraction limit be overcome? Yes. In the 19th century, Ernst Abbe (friend of Carl Zeiss and one of the pioneers of microscopy and optics) postulated that no amount of glass refinement or lens design could escape the limit of resolution for visible light, which is about 0.5Âµm. Today, we have superresolution microscopy that breaks that limit (one approach to which actually does use lenses with metamaterials).
But, I think it's likely that by the time we progress to breaking the diffraction limit, the dSLR will have gone the way of the dodo. Picture Canon's 'wonder camera' combined with a plenoptic camera, then fit that into a cell phone - that's just one step along the road...
Just to make sure I'm clear...when you say "diffraction limit", are you actually talking about the "diffraction cutoff frequency"? I ask because of this statement:
"...postulated that no amount of glass refinement or lens design could escape the limit of resolution for visible light..."
The diffraction limit is a limitation of an entire imaging system ultimately affected by the resolution of the imaging medium and the aperture of the lens. Given your reference to the wavelength of green light, I think you actually mean to refer to the diffraction cutoff frequency, which would be the point at which the resolution of a lens approaches the wavelengths of the light its imaging. As a simple matter of physics, that would be the hard limit, and literally unbreakable
in any normal optical system.
Superresolution, even optical solutions, rely either on oscillations and multiple images, or information fabrication, and while they can break the diffraction limit
of any given imaging system, I don't know that they can actually image detail beyond the wavelength of light (unless they fabricate it, which leads to a debate unto itself.)