You present some interesting ideas. With respect to moving disadvantage to wisdom, charisma, and intelligence checks I tried to think of how exhaustion feels in reality. The best example I could think of was bailing hay mid-summer. It's been several years since I've bailed hay and I didn't have to do it very often, but when I did it was exhausting work. Thinking back on that time, I feel like my mental capacity was diminished before my physical capacity. It would have been difficult to recall something I learned earlier in the week at school, or to perceive a subtle movement; but I would have had more capability to keep bailing hay if needed, until I couldn't move. This is just some food for thought.
I'm not supporting trying to apply reality to the game. It generally doesn't work well. However, Mearls did say something in his last Happy Fun Time video that made sense. If the rule feels natural to follow then applying it will be easier because it will make sense to all the players and the DM, and there will be less of a need to stop the game and look it up.
I'm not supporting trying to apply reality to the game. It generally doesn't work well. However, Mearls did say something in his last Happy Fun Time video that made sense. If the rule feels natural to follow then applying it will be easier because it will make sense to all the players and the DM, and there will be less of a need to stop the game and look it up.