Many years ago, I proposed that the airlines be required to have an auto-land/lockout feature. That is, if the plane was not being flown by the scheduled flight crew, that it would recognize this and divert to the nearest equipped military field. Now imagine that you are a hijacker. Forget about SWAT. You just messed up the flight schedule of a military organization and they are gonna be p@#$%ed.
With all of the gear that is being incorporated or required by the FAA in light planes today, much of the data is available for a decent autonomous function. The expense comes in when it is in charge of primary control, and not a backup system. Such would be the case for an incapacitated pilot. Redundancy and certification costs can be killer....
Dave