This has been discussed many times before. For a variety of technical, regulatory, social, and cost issues I think a good round number is 100 years at the earliest. It's taking the FAA 20+ years to get ADS-B implemented, and who knows how long for next-gen ATC. Those systems are barely scratching the surface of what would be required for automated airliners.

First you will see military cargo ops in military controlled airspace. eventually you will see domestic fixed-wing cargo ops maybe followed by domestic passenger ops. For international ops, you will need the entire world to re-engineer their airspace, ATC, and regulatory infrastructure...good luck.

Could it be done? Sure, it could be done right now. But somebody (ie the government) would have to spend hundreds of billions to create the infrastructure first because nobody is going to build unmanned airliner that cannot legally be flown...last I heard the feds were a bit short of cash. Also even if the FAA did everything it would need to, boeing could still not afford to build an airliner for US domestic-only operations...too much R&D overhead for way too small of a market. They would need the world on board. It's a chicken or egg problem.