Thomas Smet
Veteran
I make the opposite assumption. I would expect a m4/3 mount Sigma 18-35 to cost the same as it does for the other mounts, which would save us the cost of the SpeedBooster. That's no small savings.
Then bring that up to Sigma. That has nothing to do with m43. Yeah Sigma should make a m43 mount but you know the funny thing about that. Rokinon makes m43 cine lenses and yet most people end up buying the EF or Nikon mount versions instead so they can use the SB. You buy the SB once and don't buy it again for each lens and most people would rather have that extra wide FOV and extra stop advantage which does bring them to s35mm territory. You can also use a cheap dummy adapter so no big deal really.