The mount diameter the Nikon has is not an impediment to making super speed lenses, although that is an often-repeated myth. The Leica M mount has been the target of many superspeed wide-angle and normal lenses within the past decade. The new Nikon Z mount is quite a bit larger than the new Canon RF mount and Nikon has released some patent designs for super speed lenses. The problem comes with actually getting decent pictures from such lenses. And with increasing sensor quality and better and better High ISO performance, there is very little needed these days wider than F / 1.4..