Interesting topic. What if the first step to autonomous flight is to transition to drones? In other words, what if you can have a reliable communication channel between the plane and the ground? Then you can still have two humans flying the plane from the ground just like they would if they were in the cockpit. The shift to fly-by-wire facilitates this as all you do it tell the commuter what you want to do rather than pulling actual cables, etc. So why do you have to communicate with the computer from the cockpit when you can be on the ground doing the same, again assuming a reliable communication channel? I know the technology is not there yet, and I am deliberately simplifying, e.g. you still need to design a way to pull a circuit breaker if you want to do that, etc.
So once you transition to unmanned aircraft flown from the ground, then the threat to the pilot profession will be there, because you can then assign a crew to do the departures and arrivals in the terminal environment and then let the automation fly the rest. Perhaps a computer can monitor thousands of aircraft in cruise, and if there is any alarm coming from any of them, then a ready crew on the ground is immediately assigned to it. You can then fly a lot of planes with a fraction of the pilots it takes today.
And the threshold for any alarm can be as high or as low as you like
- weather ahead, turbulence level, smell (maybe there are sensors to detect the smell of burning wire as well as a human can), etc. Maybe even the FA can press a button to raise an alarm if something doesn't feel right if that is what it takes to make the flying public more comfortable with the idea.
Once you transition to this, then the introduction of AI can be incremental. Maybe you can trust AI to deal with some alarms and not others. As the AI technology gets better and better you have more alarms being dealt with by a computer and therefore fewer humans will be required to keep the system operational.
So the first step is to replicate the cockpit on the ground and have reliable communication as if the pilot is in the aircraft. If you can do that, the rest will follow rather quickly.