I will reply to some of the points made in the thread here and summarize them in one post:
I don't do any editing in camera or on SD card ever. All pictures are first imported to my computers hard-disk and then further processed. My computer is never allowed to write to SD cards.
Write speed is not important at startup time for the camera. I get the same results in different cameras with write protected cards. The M, switched to live view, only checks at the very end of the startup if the card is writable and displays a warning.
The Lexar Professional SDXC-II 128GB has the extra line of contacts, that are not used by the M, but without using the faster interface, I found statements, that it is still able to give a reading speed of 104MB/s, which is two and a half times faster than the card, with wich I first experienced the long startup time.
However, since some insist, that only with very special cards, formatted with only a very special formatting program (only exactly 42 minutes after full moon in leap years while standing on my head...), I also did that: a new Transcend (I'm sure, someone will say, that Transcend is totally wrong) 64GB SDXC-I with 60MB/s WRITE speed and even much faster read formatted with the highly recommended SD-Formatter program: All the same startup time of nearly 13 seconds.
Some replies also ignore the precondition, that I'm talking about: The card has nearly 2000 RAW images on it and also that many jpegs. Removing half of the images also reduces startup time significantly, but not by half, so there is an offset. Probably the about 1.4s that one can get with a fresh formatted empty card.
I also wrote to the german Leica customer service, but besides an automatic robot-answer I did not get any reply, yet. Maybe, they are too busy right now or they simply don't see any problem with 12-14s startup time, when the card has that many RAW on it.
What does seem to get recognized, is that I don't only think, that 13 seconds startup time are unacceptable. I think, there are more flaws than that. Probably the 13s don't even break the internal SW specification of the M. But then it is the spec, that is flawed. All SD cards I tried, were also tried in a Olympus E-M1 with the same preconditions. With that camera, the startup time simply were constantly fast, no matter how many pictures, if formatted in camera or not or written with the computer or not. That camera is always quickly ready. And this is im my picture a big flaw in the firmware from Leica. Also to say, the cards only work fast and good, when formatted not in camera but with a special external program is a hint of a flawed firmware. A camera should be able to format a card on their own correctly. Otherwise the firmware IS FLAWED.