Seems like a damn good idea to me. If it can be made to work reliably it ought to make more power and be more efficient with less gas.
I don't know about all that 'valvetrain contriburing to power via upper piston' stuff, as you only get X amount of power out of each power stroke. So now less is used to drive the main piston downward and the rest is used to drive the upper piston up, with less parasitic loss to valvetrain since it's a rotary valve (no heavy valvesprings to compress, less mass moving in the head).
I hope thsi takes off, because it certainly has benefits in fuel consumption, power, and it ought to keep the pistons pretty clean too! Wonder what kind of issues there are in the long term with moisture in the oil? Lots of PSI of steam, so surely some gets past the rings.