I'm not sure how feasible this is in Unreal Engine 4, but I'm curious to know if there are any long-term plans to implement in-game demo recording.
In 1.1, as I understand it this was accomplished by saving network packets into .DM_69 files that could be played back like an active network connection later.
It sounds like a trivial feature to have when you can screen capture with software like FRAPS, but it's actually a valuable tool for capturing evidence of rule violations so that warnings and bans can be issued - mainly because clients can be set to automatically record hundreds of hours of gameplay with very small disk space requirements.
I know this feature would have personally saved me a few major headaches in the past if I had learned to use it earlier, and I've managed to capture some rather unique moments with it in the time since I have enabled it that would have been lost otherwise.