The latest Apple iMac has a 27-inch 5K display with a resolution of 5120×2880 pixels. That’s 14.7 megapixels, which although less than many digital still cameras is actually 78% more pixels than a 4K image. So you can edit 4K video at full resolution within an application interface. There is clearly no need for a 4K screen to be large to be appreciated. It is more a matter of viewing context.