More than a year ago Sony did explain the E-mount size allows for very fats lens design. Still the myth about “large mount equals better lens performance” still persists. SLRlounge analyzed the myth saying that larger mounts are better. The simple answer is that NO this isn’t the case:
It all comes down to this: regardless of whichever lenses are optically possible, or even probable, that’s not even the final piece of the puzzle. The final piece is, of course, …which lenses do you see yourself actually buying and using?
Whatever slight difference there might be in the theoretical limits, or whatever exotic optics actually come to fruition, most photographers are going to be more than happy with any system. Indeed, they’re much better off choosing a system based on criteria that includes literally anything else…
There are many photographers who already know they love f/1.2 primes, of course. I just said that if I were exclusively a portrait photographer, Canon’s RF mount would be the most tempting choice, even though I could surely get any job done with any of the very impressive portrait lenses for Nikon or Sony. And, although I don’t think I’ll ever own the Nikon 58mm Noct, I’ll still look forward to seeing if Nikon makes their own 35mm, 50mm, and 85mm f/1.2 AF optics.
Sony FE could also get some of those exotic lenses, whether from Sony or Sigma or someone else. They might not be able to achieve the same level of extreme corner sharpness, as a vague prediction, but they’ve proven everyone wrong with fast glass corner sharpness multiple times already.
At the end of the day, that’s all we can say with any certainty- Almost anything is theoretically possible on Sony’s E-mount. But, maybe, just maybe, it is slightly less probable that we’ll actually see as large of a collection of “inconceivable” optical accomplishments. If true, though, it wouldn’t even be primarily a limitation of the mount, ironically, it would be simply due to Canon and Nikon’s desire to stand out.