The listed display resolutions are fed via the native resolutions that the monitor itself supports, as I recall. So if your monitor isn't a 4k one, it won't show that as a regular resolution.
That said, I've been working on the dynamic resolution scaling stuff(in cleanup/bugfixing stage atm) which allows for lowering(to improve performance) or raising(to make prettier) the render target resolution, which is done when the frame is rendered, and then brought back down to whatever resolution the window is set.
Since it goes both ways, if you have the GPU meat to pull it off, you could absolutely do 2 or more times the window resolution which would basically just be supersampling at that point.
Other optimization techniques for doing 4k without melting people's computers, like checkerboard, has had some reading done on it, but no one's attempted an implementation of it yet.