I'd like to add an argument to the chicken and egg situation we're still facing here.
1. Old facts, summarized:
FF cameras are (still) significantly more expensive and therefore, their production volume is lower. I already said that a volume-produced FF sensor wouldn't justify the steep increase in price we're still seeing. But with the steep increase in price, FF sensors aren't volume-produced (yet).
This circle installs a protection barrier for APS-C enthusiast cameras which will break away at some impredictable moment of time.
2. A new element adding to the discussion:
One reason why FF sensors are more expensive when not volume-produced is that the
photoreticle (and stepper widths) weren't made large enough in the first place. Typical values go to up to 22x30mm. But larger reticles can be manufactured if justified by volume. By consequence, FF sensors are stitched which adds to the cost. A photoreticle is a phase shift glass plate with a complex pattern.
It turns out that
Hoya is a leading manufacturer of reticles (together with Dai Nippon Printing Company, Toppan Photomasks, Photronics, Taiwan Mask Corporation, Compugraphics Photomask Solutions, Intel Mask Operations, AMD, IBM, NEC, TSMC, Samsung, Micron Technology). That's one asset of Hoya which Canikon may be lacking.
It may even be a good idea for Hoya to specialize on FF reticles and help Sony to manufacture (and share with Hoya) affordable wafers for FF sensors. Therefore, they could lead rather than follow.