I really rarely use the video option, and think that the little could be covered with my phone. So when evaluating a new camera model I don't consider video modes, just note that it's there.
But what would be the difference between a Nikon Z7 II - Still and an Nikon Z7 II - Live? Physical stuff like different lens mount, CPU, memory cards, screen, buttons, sensor? No not likely. I guess that a dedicated video would be without a mechanical shutter, and that's about it. On the software side I'm quiet sure the 2 models would be different, but anyway rather alike. Most likely the camera producer makes software modular, so some main parts of the software would be exactly the same, like menu, writing data to memory cards, controlling aperture, shutter (the electronic) and signal gain (ISO). But components to handle specific parts of video and still pictures would be handled in separate modules only being available according to model.
Would development or production cost change? Probably not with a dime.
Would the producer sell more cameras by having dedicated function models? Not likely, rather fewer.
What would happen to prices for a dedicated camera model, would a dedicated still pic camera be cheaper than today's combo model? No it is likely to be marketed at a higher price, leading to even fewer sold.
It's like buying a Swiss army knife for the lovely sharp blade and the wine screw that you uses over and over again, but never touches the can opener or the scissors. it doesn't make the knife poorer or useless, you just have an extra option if you decide to use it some time