VCM may not be that cheap to add on. The assymetry of using 3 cylinders causes engine vibrations that have to be dealt with by adding stabilizers and dampening. So there is cost, and weight.

An otto engine is efficient around 50% of max power output; so in the case of the over-powered Odyssey, even 3 cylinders is too much at highway cruising speeds. Without a hybrid configuration, the engine must operate at a low rpm, inefficient power range.

Perhaps an 8 cylinder, 15 bhp/cylinder configuration would do better.