seems to me it would vibrate....
If you ran just 2 cylinders, the engine would definitely be seriously out of balance. My first impression is that a 4 cylinder version would not be nearly as smooth as conventional 4s, as you still could not balance the forces and moments as well. A flat 8 from this could potentially be pretty smooth, though, as that's the point in which you could balance forces well. A Y6 might be an option (not V, but Y)... but I haven't done any calcs....
That was my first thought too, but now I'm not so sure especially for a multicylinder version. As I look at the cam rotate, I see two lobes of the cam at BDC each time the piston is at TDC. It might balance out. One thing is for sure, I'd love to hear one run.