You can tell xrandr anything, it doesn't have to be physically connected. So you could get 3960x1080 virtual screen space for a single vertical HD screen. If you move your mouse to the edge of the screen it will scroll what is visible. I discovered it in my triple monitor setup. I turn off screens I don't need (they waste like 30W!), but the script I wrote to notify X11 of these changes doesn't work as reliably as I would like, lol. Also duplicate polybar sometimes, haha.

Not sure how useful this is, because while the application thinks it has all this screen space available you can't actually see all of it at once.