Back in the day (film), the depth of field preview button/lever was a nifty way of assessing what the camera would see based on lens aperture, etc. It was necessary because lenses needed to be fully open to enable manual focusing, especially in low light. In today's modern age of digital sensors and live view, the cameras have no trouble giving us a nice live view at even very low lighting levels.
I have been using some Zeiss M-Mount lenses on the Z7 with a dumb adapter, which means the lens setting is what I am viewing in the live view. I really like this ability to see the depth of field live and wish I could do this with my Z-Mount lenses.
So now, why not have a DoF preview setting (on/off) instead of the archaic button which needs to be depressed to be active. I would leave it on most of the time so I could see exactly what the sensor sees. In todays' cameras it's just a software implementation.
Anyone have a connection at Nikon...
JM