The saab variable compression engine doesn't have a head-block setup. It is just one piece. It uses a mild supercharger and under cases of heavy load (standing start )uses mild (10:1) compression, but if you at light load (highway cruizing) it rotates the head and decreases the combussion chamber size to increase the compression(over 16:1!) Variable displacement is a long way away still, and probably not economically feasable. Rod's and cranks need to be very strong to take the harmonics of engines. At 9,000 rpm things inside really start to dance, and sliding hydro pins, and other sorts of goodies would not be nice. As for the wankel thing, mazda has a 'patent' of sorts on it, prohibiting other manufacturer's from persuing it too much!