Pilots nodding off, particularly on long haul, is a perennial problem. Maybe the proper solution is a pragmatic approach.
One of the guys at the Orval recalled a certain European airline, engaged mostly in trans-Atlantic flights, that addressed the problem by fitting a loud egg timer to the overhead panel.
Apparently rest periods of about 30 min. were recommended and, coupled with standard cabin staff visits every 20 min., seemed to work very well. With all crewmembers arriving at destination maybe tired, but not fatigued.
Crew are not automata, legislation up to the eyeballs will not provide solutions.