Currently, the multi-monitor support is quite lackluster. There's a few things required to get it to a fully usable stage:
1. Ability to deactivate a screen after it's been activated.
2. Ability to fully control full-screen window after multi-monitor activation. At present, activating a second screen forces the primary window to fullscreen, and setting it back to windowed mode removes the top window bar
3. Metal support for MacOS. There is still no support for multi-displays when using Metal on Mac. With OpenGL being depreciated on OSX soon, Metal support is essential.