Aircraft without cabin crew already flying around : <19 seaters in the US, and some CIS States for flights less than 1 hour.(you get a briefing on how to open the emergency doors in case emergency )
Now if you meant without ATC : everyone tried. the FAA with the MITRE Corp Area3 in the late 80s, and in Eurocontrol(Bretigny) with Mr Maignan wondermachine around the same period. Both failed miserably because they could not increase capacity. The final thing is : you can only automate the rules, and only human can bend rules.
It is a fact that is far easier to automate flight than ATC.
So if you like to plan the future , then I can safely bet with you that there will be pilotless aircraft before there is fully automatic ATC.