Erik,
That is a good point: AFAIK, diffraction transforms the image in a reversible way, so that with sufficiently high resolution, the right sharpening transformation could undo it completely. Though the algorithm might need to know a lot about the particular lens, like the shape and position of the aperture diaphragm.
So perhaps the ultimate landscape camera of the future will be a massively oversampled pinhole camera (no aberrations!) backed up by enough computing power to unravel the diffraction.