Descent 4 w/ Oculus Rift support. Will probably never happen. It should be bundled with a coupon for free Dramamine.
I would like to see a puzzle game like Portal, but where there's time travel between the portals. The engine sees the trajectory the ball is going to take, and lets it fly out of the 2nd portal a couple seconds before it enters the first one. Self-consistent paradoxes would be the solutions to some of the puzzles. You press a button, and you launch a ball. The ball isn't going to make it to the portal, but right before it would miss, the counterpart ball (from the future) flys out of the 2nd portal and hits the ball into the 1st one, and gives the remaining ball just enough of a nudge that it can reach the button that triggers the exit. If the player tries a non-consistent paradox (like the ball from the future prevents the ball from going in the portal), then there's some severe penalty, like the universe implodes or something.