Those that think nothing has changed in the last 20-30 years have forgotten the single most important thing that is driving self driving vehicles, navigation systems. The self contained navigation system that with very little input can guide an aircraft from gate to gate without any issue. GPS is already accurate and reliable enough for all aviation applications. This can be further be refined to cm accuracy using mobile phone towers alone, forget needing fancy GBAS. The future is already here, and they are developing it agressively.
Just because we've stuck with two pilots for 30 years means nothing much. Trains had two drivers, stoker on the foot plate with multiple conductors and brakeman for 100 years, now theres only one driver and no one else. In reality trains could easily go crewless tomorrow, just needs a bit of spending.