I think there's some pretty bold statements made here about what's possible and not. @Spacecat (& Les) - it sounds as though you have some misunderstandings about planetary image processing, not helped by 101 statements such as "over -sharpening can introduce artefacts", well yes of course! We all try rather hard to minimise that, and methods have come on quite a lot since early image processing programs.
First of all, the key relevant issue that we encounter with imaging planets is a diffraction rind effect on very hard high-contrast edges - the issue is most pronounced off some higher surface brightness objects such as the limbs of Venus and Mars, lunar craters, Mars' polar cap. The issue is wavelength-dependent and can create unnatural light/dark banding in some areas of some images, perhaps
best discussed by Martin Lewis here. The diffraction effect is present in raw data, and is (importantly) not a processing artefact. Well-processed images these days show few true "processing artefacts", though this can be very hard to do!
The diffraction issues are not generally so much of an issue for Saturn's rings though, otherwise we would expect to see it all the way around the rings. I think this is because Saturn's surface brightness (even the rings) is lower than surfaces where we commonly see the edge-rinds. But is it of course plausible that this explains some of the images with Encke-located brightness minima, but I'd argue that this is not typically the case, especially where we don't see such a deep brightness minimum from nearby harder edges, such as the Cassini Division, or on ring edges away from the ansae. Ultra-minimally processed stacks of Mars and Saturn are attached (so high noise), with the bright limb of Mars showing the diffraction effect, Saturn's rings show it a little on the highest contrast outer B ring, but not elsewhere.
The second is that what we see at the ring ansae is very consistent with what is seen in larger scopes - see the attached example with Hubble,
Pic du Midi,
Tiziano Olivetti,
Damian Peach and myself. It's obvious that Hubble resolves it, it's pretty clearly visible in the 1m (Peach processed same technique as C14 images) and 505mm images, but likely not truly resolved in either. The darkening appears consistently in C14 images such as mine and Peach, consistently in the right regions to not be a processing artefact. I would draw your attention to my ultra-soft processing sample of a single 1min red stack which, with the barest of processing immediately shows the minimum brightness at the correct region for Encke, and not elsewhere. This demonstrates that it is a real feature of the data and not an artefact by overenthusiastic image processors!! That it only appears at the ansae, at the correct location where we would most expect to observe Encke, and not from the brightest hard edges in the image strongly suggests it's not a diffraction effect (one of those is faintly visible in my raw frame on the outer edge of the B ring).
Should it be visible - well, yes!
It is not truly being resolved in our images, probably not even in the Pic du Midi image. But it is helping to darken the pixels that otherwise would be smooth equal brightness across the outer A ring. So it is increasingly prominent as this darkness becomes a large fraction of the resolved pixels as imaging resolution increases. The example I've also put in is the Hubble image, resampled to 15% (about 3.5px/", and close to a decent amateur scope resolution), where the original Encke would be <1/3 a pixel in width. You see very similar ring features in the resampled Hubble, Damian's, Tiziano's and my images, including an Encke minimum. And our wavelet processing will bring out this minimum in brightness. So we're not "resolving" it, but we are genuinely imaging it, rather than a pure artefact. And it's fair to say, if we're not imaging it, then visual observers definitely are not seeing it!!
[worth noting that Chris' processing is stronger than many imagers, as he is aiming to bring out low contrast cloud features on the globe, and is distinctly overprocessing the rings in his example posted, he's not all that bothered by the rings]