It seems that Canon has different priorities. According to DxO-mark, the Nikon cameras using on chip converters gained a lot in DR, why development in DR was little at Canon. DR is the factor mostly negatively affected by reducing pixel size.
Canon already has the 7D. Would that sensor be upscaled to FF it would offer 46 MP. So Canon could do it.
My guess may be that Canon has slightly different focus than Nikon, geared more to high ISO, where they are very good. I guess that landscape shooters using tripod at base ISO are a minority.
"So, back to the rumors of Canon allegedly readying a high resolution competitor to the Nikon D800 . Will Canon finally move off that 0.5 µm generation? It is worth noting that September 2012 marked the 10 year anniversary of Canon’s announcement of the world’s first CMOS FF sensor, the EOS 1Ds. While Chipworks didn’t analyze that camera, every Canon FF sensor analyzed since has used the same 0.5 µm design rules. It is a credit to Canon that it has remained competitive by continuing to optimize its pixels fabricated in a relatively mature process.
Canon does have a 0.18 µm generation CIS wafer fab process, featuring a specialized Cu back end of line (BEOL) including light pipes (shown below). It is possible to speculate that Canon may be preparing to refresh its FF CIS line to supply devices for a new FF camera system. Samsung and Panasonic currently use Cu fabs to produce APS-C and micro 4/3 CIS devices. It seems that Canon is destined to do so for APS-C and perhaps ultimately FF. Part III of this series will discuss CMOSIS/STMicroelectronics’ combined effort to produce FF CIS using sub 0.18 µm design rules for the first time.
Aside from the pixel process, there are also design considerations for Canon. Of the Canon DSLRs analyzed, the imaging chip has remained analog, with Analog Devices’ analog front end (AFE) chips handling A/D conversion en route to the Digic-branded ISPs. Perhaps the column-parallel ADCs favored by others can’t be implemented using 0.5 µm design rules, but more likely Canon is satisfied with its system design and performance. In the spirit of speculation, if Canon does migrate to a more advanced node for fabrication, could the transition coincide with a major overhaul of the CIS and system design?"