the optical viewfinder is a big argument for me to use the Leica M.
I know there are people now who prefer EVF, but there are also many who do prefer optical viewfinders.
I also believe there are many people who do like a simple and "analog" style user interface - and here the Leica shines.
For those people who do like EVF, and who do like AF the Sony looks like a nice alternative...
The lenses they announced seem to be a usefull compromise between speed and size which I think is good. And I am sure they will add some more special lenses and faster glass later.
For my part, after going though all kind of stuff (M9-m43-x-pro1-rx1-M) I still found no mirrorless which I prefer over my digital Leicas in regards to user interface AND IQ. I love the 35/1.4FLE and the 75/2.0 as well as the 21/3.4 and 50Summicron/Summilux.
And I almost allways use the rangefinder. Have tried focus peaking, don't like it. Same with magnification and framing and switching back and forth.
If I would use the new FF Sony I would want to use it with AF.
I think your impression about problems with the "M" doesn't reflect reality.
The M is a damn good camera and most users are pretty happy with it. The biggest issue is the delivery problem IMO.
I still believe the FF Sony is a great option and some competition in the FF mirrorless market is good for Leica.