Even the very modern trains still have a pilot there , so I think it will take a bit longer in aviation.
Looking at train operators in the US of A, you'll find that the long distance freight and passenger trains have
two engineers up front.
Besides single-pilot being a certification issue I can also see insurance companies raising an eyebrow or two. Not sure how the traveling public will react with a single pilot up front.
Why are we so obsessed to replace humans with machines, anyway?