A few other notes besides the fact that many companies have been doing this for years already:
1) It really doesn’t save much gas. Some? Yep... but nowhere near 50%. 5-10%, tops....
2) They have been reliability nightmares in the past.
3) Even on new versions, owners tend to despise these systems after having to live with them for awhile. You can put on fancy noise cancelling systems to smooth the switching and kill the noise, but you can’t defeat one simple principle: The engine is no longer well-balanced when running on a limited number of cylinders. If you take a V6 that has been properly balanced and change it to a V4 or V3, it is no longer balanced. You’ll get extra vibration and torque on its mounts. What was a wonderfully smooth Accord V6 is now a rough Accord V3. The companies have all done fantastic jobs minimizing the impact of this imbalance, but it simply isn’t as nice of a feel.
Why don’t they put the old Mitsubishi silent shaft on it?