I was just speaking with a Canon Rep today at a photo show and I asked him about the 10mm-22mm lense, he said that it was the sharper of the 2 new lenses released (the other being the 17mm-85mm IS) by a large margin. He also said that he had spoken to one of the Canon engineers about the 10mm-22mm and he had said that the picture quality was L quality but the build was pro-sumer quality, he had also said that the lense was supposedly designed as an L lense but at the last minute they changed the plan and kept the glass but ditched the robust build and the weather sealing. I do not know how much of this is accurate but it makes sense, if they made it an L lense they would be competing against themselves for the most part as L lenses in that range already exist that can be swapped between bodies in contrast to the S mount which cannot.
Canon 1DsMk2, EOS RP, Canon 17-40 f4L, 24-105 f4.0L ll, Canon 70-300 f5.6L IS , Sigma 85mm f1.4