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.