TL;DR: You can't really replace a monitor wall with a single screen because it does not curve to create the right viewing angle, which makes text seriously unreadable at the edges, which forces you to seriously upscale the font size, which steals the largest amount of real estate possible. Of all the compromises to make, reducing the number of screens is one of the worst ones.
4k screens are already somewhat questionable for productivity for this reason alone. The only serious argument that can be made is 1440p vs 1080p (personally I would argue for 1080p, if using bitmap fonts and having perfect eyesight). A 4k monitor wall is a rather fringe setup, that only works out to an advantage for day traders and weird surveillance applications. And it requires that you constantly do very energetic body gymnastics to change your perspective's location and be able to see all the details. With a single 8k screen without upscaling font size (hence preserving all technical real-estate), the body gymnastics required would be so much worse than a 4k wall, it would be absolutely ridiculous and clown-alike and almost impossible to use while typing. Otherwise people mainly want big 4k/8k screens for dual use as a TV set. But this is just wrong in itself, it creates a paradox for no good reason, like using screwdrivers as chisels. Some things are not meant to be. The only arrangement where 4k makes some sense for common use cases, is maybe above a curved ultra widescreen.
4k screens are already somewhat questionable for productivity for this reason alone. The only serious argument that can be made is 1440p vs 1080p (personally I would argue for 1080p, if using bitmap fonts and having perfect eyesight). A 4k monitor wall is a rather fringe setup, that only works out to an advantage for day traders and weird surveillance applications. And it requires that you constantly do very energetic body gymnastics to change your perspective's location and be able to see all the details. With a single 8k screen without upscaling font size (hence preserving all technical real-estate), the body gymnastics required would be so much worse than a 4k wall, it would be absolutely ridiculous and clown-alike and almost impossible to use while typing. Otherwise people mainly want big 4k/8k screens for dual use as a TV set. But this is just wrong in itself, it creates a paradox for no good reason, like using screwdrivers as chisels. Some things are not meant to be. The only arrangement where 4k makes some sense for common use cases, is maybe above a curved ultra widescreen.