dead end is a generous description. this system was still born - Canon shoved it out the door ... Now you're in
a "pasting feathers on a turkey" mode and you might be better off kissing it off and starting from scratch.
The EOS M was the second best-selling MILC in Japan last year. One country's meat is another one's spoiled turkey...
I just wonder how many Japanese buyers buy it with only one lens and will never even put another lens on it. Of course, as I recall, the average number of lenses owned by Canon DSLR buyers is less than two.
There are many people who would buy it without any EF-M lenses. They only care about adapters for lenses they already have, like Canon EF. That makes a lot of sense for telephoto, because there are no small CSC tele lenses without huge compromises in IQ. EF-S 55-250mm IS STM can be considered "near native" lens for EOS-M (via the adapter) - fast AF, nice optics, stabilized, compact (for 88-400mm equivalent ) and affordable. Many are using old manual lenses and they love it.