There have been a number of posts regarding support for outputting to multiple displays from one or more in-game cameras:
- Multiple camera's ingame, display output on multiple monitors - UE4 AnswerHub
- Multiple active cameras for 1 player - C++ Gameplay Programming - Unreal Engine Forums
Extending the engine is not only cumbersome, but from observing the threads above, people seem to have a limited rate of success, and even then these efforts are likely to break with engine updates. While this type of configuration is natively supported in Unity and very easy to setup for non-standard display configurations, Unreal is a superior engine in many ways, and there is and has been clear community interest in this topic.
Can Epic please implement native support for this?