Now that Leica have the new SL many are saying that this also will be the death of the Leica M. It seems that too few people understand the strengths of the rangefinder and its limitations.
The biggest draw to Leica is of course the Leica glass and many use that glass on their Sony’s, their Olympus/Panasonic’s and their Fuji’s.
Because of the design of a rangefinder lens the ultra wides generally give colour shifts and odd corner artefacts on any camera that is not designed for rangefinder lens, so if your interested in using lens wider then 35mm you need to either use a Leica M or the Ricoh’s A12 M-Mount module for the GXR. Even the Leica SL and T have these issues with wide rangefinder lens.
The key feature of a rangefinder is its optical viewfinder, being able to see more of the scene then you will photograph, if you shoot reactively, and with wide lens, then a rangefinder maybe for you, and an EVF unsuitable for you. If however you shoot more planned and carefully such as landscape, portraits and architecture, need to see precisely what you are shooting then the EVF or traditional SLR is better for you. Certainly if you commonly shoot 50mm or above then a modern mirrorless or SLR is a better choice.
So will these cameras be the death of the Leica M rangefinder, no. But I will say to make the M more flexible I would like to see a hybrid viewfinder like in the Fuji cameras, the best of both worlds. Until them many people like me who shoot many styles then we will sometimes carry our Leica M and sometimes our SLR.