What my fellow passengers wear on board is certainly none of my business. I might be amused and
envious 
at the pax, who appears to still be wearing pajama attire and clutching a pillow as they board. Good for them.
For business travel, I am always "Business Casual" or full suit and tie, depending on what my appointments dictate on arrival. No choice. And I only travel domestic US for business, so no extreme long haul flights.
For leisure travel, I dress for the destination and comfort.