I think it would be amazing if the HUD was not just 2d elements superimposed on your screen, but 3d models with distance. It would be cool on a standard monitor, but would really shine on an Oculus Rift where it would really look like there is a compass floating in front of your face, The Witcher did something like this with the amulet in the top let of the screen.
It would also be cool the inventory menu was done in complete 3d, where you are looking at a 3d shelf with all your items, and Henry standing beside the shelf so you can see what you look like. The game “The Forest” has done something like that with their inventory system.
The Forest inventory screen