Make one monitor move/display different screens as we move mouse around different physical displays

I have a computer with two hookups from the same GPU to act as a dummy connection for steam link/steam remote play so it's the correct size since the base monitor is 32:9 and I need closer to 16:9 for the tablet running steam link.

When using steam link and moving the mouse between the "monitors" it moves the windows and switchs displays to the two different screens. So, as I drag between a 2560x1440 and 5120x1440 destkop from windows and it changes the size of the screen on the tablet and allows me to quick move between each seamlessly just by dragging windows between different screens or just by moving the mouse.

It might need some things added so you don't overly switch in some software too easily, but could this be added as a feature of windows with logical screens/desktop that are hooked to the physical connections from the gpu/cpu/etc and seemelessly flip signals on a single monitor? Or however that could be done.

It's insanely convenient and when I went back on my PC I kept wanting to do it physically and notice the lack of it. It could make a very nice display feature for windows in general. Especially since everything has multi desktop also.  Then there could be multi hardware and software switching. 

How does steam do this? What features could be derived from this?