A very early first look at the game will be streamed live on Twitch tonight at 7pm UK time / 2pm ET. I'll be going into some of the technology that's been created for the game, and showing off a bit of the gameplay. It's not a trailer, it's not a demo, but it should give you some idea of what's in store:
https://forums.unrealengine.com/t/inside-unreal-taking-pcg-to-the-extreme-with-the-pcgex-plugin/2479952
You can also watch the stream on YouTube, and there'll be a version archived as well
https://www.youtube.com/playlist?list=PLZlv_N0_O1gbggHiwNP2JBXGeD2h12tbB