I agree with Roger in that digital Leicas are not just bought because people either (a) misguidedly think they are best or (b) want a status symbol. As hard as this is to believe, some buy them because they are technically good enough, while delivering a user experience that (for some) strongly encourages the act of photography and the improves quality of the results.
Thew new Sony does not threaten Leica as such, but may steal M240 sales with those fed up of waiting. The A7 series may also steal sales from those who want amazing quality in a small package and are not too bothered about rangefinders and the true manual focus feel. This latter point is still an area where Leica does lead the way and why Leica has not been quick to give up on the costly and finicky RF viewfinder. It is also where Fuji is potentially dangerous, but both Sony and Fuji have their pros and cons.
Were Sony or Fuji to produce a FF camera of this kind with an optical finder of the size and quality of the Leica, that was designed around compatibility with M lenses and the flange focal distance entailed (as well as their own lenses), I do think Leica would be in trouble. Were they to build it with a truly premium shell, keep the menus and buttons simple and price it at perhaps $3,000- $3,500, very few Leica fans would not look elsewhere, because the utility requirements would be met. But they haven't and the difference between my MM and the new Sony is still substantial.
That said, I am very interested in the Sony because I do not have a small FF interchangeable lens colour camera and cannot afford a M240 on top of the MM I already have. If I do get one, there would be a slender possibility I would then sell the MM, but have a strong feeling that the relationship between me, the camera and subjects would not feel the same without the optical finder and so would keep the Leica for the majority of my work.
Especially if your pictures are rotten, and all you care about is corner-to-corner sharpness.
At another point, what counts is whether the camera feels like an extension of your hand end eye. Maybe that's one of the factors keeping Leica in business, and the sensor and the lenses are secondary. .
Cheers,
R.