"Hybrid Synergy Drive" minus the electricity..
 

Toyota's hybrid system uses an atkinson cycle engine mated to an electric motor through a variable transmission..

But what if this idea was combined with the idea of variable displacement engines? For example a two cylinder atkinson cycle engine which runs accessories (alternator and such), mated to a two cylinder otto cycle engine through a CVT so that the system as a whole performs effectively as a variable displacement engine - the otto cycle engine could shut off entirely when torque isn't needed, and get "bump started" by the continuously running atkinson engine whenever its power is required.

The advantage I see over current cylinder deactivation schemes, would be that dormant pistons wouldn't need to be in motion (or at least, moving as fast) when active pistons are operating - and continuous load accessories like AC and electrical could be operated by a more easily optimized atkinson cycle ICE.

So.. that's my thought - I don't have the means to bring it into reality, but I welcome discussion. :)

You'd want a common cooling system to keep both engines up to temperature, and you'd probably want a common oiling system for the same reason. At this stage it looks like you'd be adding needless complexity, but once it's implemented smoothly it could work really well.

Why an otto cycle? Isn't the atkinson cycle more efficient?