When will websites fully support 4K?

LinkedIn, for example, does not support dynamic content on 4K displays. It barely copes with a 2K display.

LinkedIn on 4K UHD (3840x2160) at 100% on Ghost Browser 2

Ghost Editor does not fair much better on 4K displays.

Ghost Editor on 4K UHD (3840x2160) at 100% on Ghost Browser 2