Could engines run on 1 cylinder while idling to save fuel? And then either each "idle" session alternate a different cylinder so wear and tear is even, or change the active cylinder periodically throughout an idle session (i.e every 1 minute idle, change the singular active cylinder). I realize that this is probably pointless with modern start / stop features on many newer engines, but why wasn't my idea possible before we came up with the tech to enable modern start / stop on engines?
If you shut off the ignition for the cylinder you wish to disable, the action of the piston rising and falling in the cylinder (with no combustion) will tend to load the combustion chamber with motor oil, which then fouls the spark plug- so that when you want to turn that cylinder back on, it refuses to fire.
That puts the driver in a perilous situation, if (s)he were trying to pass another car on the highway. You are cruising along with cylinders idled, then you pull out to pass, step on the gas- and instead of the idled cylinders suddenly "waking up", the engine stumbles, bucks, misfires and smokes. Yikes!