Speed is traded off for resolution. The thicker the paper, the more it would absorb the ink, and the less would rub off. I would not recommend this for thin (2 layer) paper.

If you are actually interested in doing this, I'd be up for doing the project. I actually have the motors, motor drivers, microcontroller, and inkjet cartridge full of red ink already. I also have a 3d printer for mechanical prototyping, and a good supply of toilet paper. If you are interested in working on this with me, email me at kliment.yanev at gmail.