For me, the lack of weather sealing by Sigma is the lost opportunity here.
Yes, I know the Canon 35mm f/1.4 L is not weather-sealed. But the lens is old enough where it makes sense to me to wait and see if they release a weather-sealed update any time soon. If the Sigma had been, I'd not hesitate for a second to pick up a lens with better IQ at a significantly lower cost regardless of what Canon has up its sleeve.
So if Canon comes out with a new version that costs $2000 but with weather sealing, you're ready to pay more than double? Good job.
Canon has a LONG history of making $2000 lenses that don't out-resolve their predecessors by a long shot and only carry weather-sealing. Good job.