It is just a idea for a shape mod that I didn't manage to build, in case someone else finds it interesting.
The idea is to obtain two fused cubes like them:
fusedCubes.JPG [ 21.21 KiB | Viewed 597 times ]
It could be modded from a rubik's cheese, where each of the pieces of the cheese corresponds to an edge of a cube, and the central plane of the cheese is the line in red here:
fusedCubes2.JPG [ 21.76 KiB | Viewed 597 times ]
OK, photos aren't good but the idea is easy
(Of course these pictures are from a cast puzzle, not a twisty one)