Just to add. I thought of this after writing up the latest patent application I was reading today.
Canon's fabs more than sales may be dictating camera releases. Canon isn't going to release a popular camera until the sensor yields are where they want them to be.
So all these timeline rumors even from last year, could have been true - at the time.
But as things progress, and if the fabrication plants are struggling with yields, that shoves the entire timeline back until they can get things up to snuff - or enough sensors produced for the camera side.
I forget what paper or patent .. but it was completely unrelated Canon has dropped down to around 50-60nm in chip tech currently from what their patents were describing. this is a huge step from around the 95;ish nm they were the last time it was communicated anywhere.
And that doesn't include ADC and signal processing layers which usually use smaller geometries - if Canon doesn't have the equipment really to do any of this, then they have to do multi-patterning to create smaller design rules with older equipment.
As Canon works on faster sensors, they have more of a challenge to control heat, timing, and power requirements. Advanced stacking, more layers, etc all come into play.
So this could all come down to an engineering problem that Canon is working through for the R1.