NOTICE: You must use version 3 or above with patch 3641. Previous versions of DualScreen do not work with 3641.
Inspired by partytime's mod Party UI, I decided to try my hand at optimising the game's UI for using splitscreen. The Party UI mod does a good job of this, but I wasn't looking for the other features that went along with it and the layout changes felt too incomplete for me (sorry partytime). I wanted the same experience in split screen that I would get if I used the native dual screen functionality (that just so happens to cause tons of crashes).
This mod will cause the game to automatically switch to split screen mode when you start a game, and that's about it. It manages the UI so any time you enable or disable the split screen mode it will automatically adjust the UI to match (including hotbuild). You can choose which monitor your UI appears on by typing /leftMonitor or /rightmonitor into chat. You can toggle whether the game will automatically switch to split screen mode by typing /enableAutoSplit or /disableAutoSplit into chat.
The latest version is DualScreen V4 DualScreen V5 in the mod vault. You can also find the source on github here https://github.com/CodingSquirrel/DualScreen
To get a true dual screen experience combine this with tatsu's script here. In particular look at the script I posted, which due to the WinRestore call will make it windowed borderless across both screens.
Limitations: I don't know how to fix an issue where if you have the right monitor selected, then it will zoom in on the left until the UI comes up, where it will just swap the two cameras. Also, I wasn't able to fix the non in-game interfaces, such as options and main menus. I may revisit this later if I find a good way to do it.