There have been several threads in the past about one man cockpit and pilotless planes. Such technology is still not available, and furthermore there are several barriers to make this happen anytime soon. But I do believe that we can get there in steps rather than strides.
If we look at how we got to the two man cockpit, we did it by first eliminating the radio operator, then the navigator, and last with the flight engineer. Perhaps it can be possible to design around the duties and functions of a relief/cruise pilot for ultra long haul flights by: (1) autopilot never disconnects and (2) A/P can fly any situation including emergency decent after depressurization, (3) fire situations, (4) multiple system failures, etc. All this automation would give warning bells to the crew who are resting in close proximity (i.e. underneath the cockpit floor) to come out of their bunks, back into the cockpit and take over if required within ample time. The savings would not be enormous but measurable: crew training, scheduling, staffing requirements, additional space available in the plane for cargo or pax, etc. Imagine if Boeing was to put this technology on the 747-8i.......I truly believe the next step towards pilotless cockpits is to relieve the cruise pilot.