Also at the Xbox Showcase, a non final version of the One X patch for Quantum Break was capturable. This patch was still very unstable, with multiple crashes during our few minutes trying it out, and hopefully also still some optimisations to come as the framerate wasn't stable at all. Also worth mentioning, our video has sound issues due to a capture problem.
Update: At the request of a few people I've added a HEVC version of the video, which should be playable on most 4K TVs directly. Tomb Raider video to follow.