I've seen some 3d printed 6dof imput devices before but they always sacrificed the UX in some way (by for example using a wheel for one if the dimensions). This is the first project I see that has a simmilar UX to the commercial 3dconnexion SpaceMouse line of products. Awesome!
I've been working on of these for a little bit as well. I have a prototype that's working, but has a few problems I hope to solve in the next iteration.
Mine is based on a Stewart platform with strain sensors for each truss.