I realised that I might offend somebody, but posted anyway. Canon have to support two lens mounts. That is probably unsustainable. Nikon's solution I think is sustainable but the Z mount does seem a bit over the top for APS-C. I agree that in five years APS-C (and full frame for that matter) will be mirrorless. If a Canon M user decides to go full frame then there is no simple migration. The user has to change everything. Its as easy to move to Sony or Nikon as it is to Canon R.