Back in its youth, the Sony full frame line of cameras used continued production of older models to accomplish price stratification that would maximize revenues. But with (much needed) improvements to ergonomics and menu structure, rolling out with the new models, this appears to no longer be as desirable to would-be buyers looking for bargains.
Industry observers suspected the newly-released A7C was meant to package the older technologies, but wrap them in a more pleasant user experience, and this appears to be the case, as Bill Claff’s amazing Photons to Photos site published data showing, indeed, there is no significant difference between the sensor from the A7 Mark III sensor released in April of 2018. Of course, the A7 III’s sensor has been fantastic, so this is should not turn off A7C buyers.
Looking forward, this may indicate the end of Sony’s policy of saving costs by simply not bothering to design a new low-end body (more likely); or, if not, that the A7C would be the offering Sony puts out instead of an A7 Mark IV (less likely).