Maybe like a super versatile trackball? Just guessing here.

Id imagine a flexible skin added to the outside of a robot containing lightpipes or fiberoptics coming back to a camera. This lets you detect collision on the outside of a robot at 30-60fps extremely cheaply. Cheap passive collision detection is missing from robotics and this is a step in the right direction. With multimaterial 3d printing you can make a wide variety of different shells for robotics which can automatically detect failures, collisions, damage and stress for the cost of the plastic and a camera sensor.

6 DOF input device using just a camera and blob of silicone? So <~$1?

"How would you use it?" is the entire video's point.

Now, what would that look like in practice. I think you should first forget about the form factor. I think the use of a smartphone (at this stage) is mostly convenience. The best lens/sensor/cpu/gpu combos are sold in this package.

When the first webcams came out, I think I would have been skeptical if someone told me "this will be a mouse soon". Today, most mice are basically very VERY low resolution webcams with buttons[1]. Maybe a new type of controller, musical instruments, or an entirely new thing will come out of this... Or nothing much, like the two research paper mentionned. In a mouse form factor i think it could be use for some of the functions of a spacemouse[2].

[1] https://en.wikipedia.org/wiki/Optical_mouse#Optical_sensor

[2] https://www.youtube.com/watch?v=iHBgNGnTiK4 ( I Made my own Space Mouse for Fusion 360 using Magnets (DIY) ). Just check the intro to have an idea on the use of spacemouse.

Most work was done as a part of my day job. It took about half a year. Significant amount of that time is for writing an academic paper. Same content as the blog post, 10x less readers, 10x more time...