You raise an interesting issue. I will say at the outset that nothing about the 80/20 approach requires athletes to train more. In fact, almost the opposite is true. Athletes gain more benefit from any amount of training they choose to do by adhering to an 80/20 intensity balance.
With my one-on-one clients, I pay close attention to sleep patterns and consider them in planning training. Self-coached athletes need to take responsibility for their own sleep. All I can say is that I would never encourage any athlete to sacrifice sleep for training. I should probably hit this topic in a future blog post!