This decision is yet another sign that the status of the M system in the current Leica portfolio is changing. The focal length of 135 mm was the longest that the Leica rangefinder could accommodate. This focal length was introduced in 1931. It was necessary in those days because of two reasons: enlargement of the scene that was at a greater distance from the photographer and it maximized the information content of the negative. The emulsions in that period were rather coarse grained and making full use of the negative area could minimize the need for big enlargements. The 135 mm was quite popular and when the M3 was announced the rangefinder was constructed such that the 135 mm could be used with some focus accuracy.
In current times the popularity of the 135 mm has been reduced and the rangefinder magnification from 0.68 to 0.73 did not allow the use of the 135. In current models the frame lines of the 135 are not included. As was the case with the R-system, the role of the 135 mm has been integrated in the several Vario lenses, now for the SL and presumably for the TL/CL too.
The 135 mm signified the universal appeal of the M-camera with focal lengths covering the range from 18 to 135 mm. The dropping of the 135 mm leaves the 90 mm as the longest focal length for the M-system. To be honest, even this focal length is a challenge for the accuracy of the rangefinder.
The M-camera has been framed today as the best for available light and street photography where the 28 and 35 mm lenses are most popular.
This whole idea of a camera suited for specific purposes is an anachronism at best. The digital cameras with a high efficiency and a high sensitivity sensor, AF and motor drive can handle almost every task and support any intention of the photographer to record a scene or express him/herself.
The M-system, once the backbone of the Leitz and Leica companies, is in danger of becoming a niche product and while still being a cash cow for the company, has no future and will not generate new sales. The annual sales of between 10,000 and 20,000 is not enough to increase the revenue to the level that the company owners and managers want to generate. The fact that there is a new edition of the Thambar and a discontinuation of the Apo-Telyt is significant. By the way: with the disappearance of the 135 mm the classic name of Telyt also vanishes.