It is not just the aircraft fleets that would need highly developed AI. ATC would as well, with backups for backups to achieve adequate margins. Perhaps this would involve internet like layers of redundant autonomous capability between individual aircraft in case of datalink loss. Until ATC becomes automated and digitised then the current analogue method of R/T between humans is the only way to manage traffic in high intensity traffic situations.
As far as product liability being an obstacle: why would an AI component be different to any other component? None are perfect yet we still have airliners.