So I came across a nasty issue with the closed source nvidia drivers: if you enable TwinView through nvidia-settings, you automatically lose xrandr support:
This is something that supported pretty much universally outside of Nvidia drivers! Even fglrx has no problems with this. Now, this may not be that big of an issue for a regular desktop, but I'm developing a library that must support mode switching.
$ xrandr -s 1
Failed to change the screen configuration!
The recommended solution is to use the old XF86VidMode extension instead. However, before I go on and add a separate code path just for nvidia drivers that can't be bothered to support modern APIs, maybe there is a simpler workaround that can get XRandR to work on Nvidia w/ TwinView?