This Samyang is not good for M.
Canon need to make native 50 for M, this will boost M sales.
I would also like(I know they won't make it):
75 2.0 IS macro(not 1:1).
100 2.0/135 2.8 small telephoto/portrait lens.
50-125 2.8 IS good quality telephoto zoom which covers 80-200 FF distance.
With lenses like that and upgraded M3 body I would use my DSLR only for birds.