I can't get behind an 'exhaustion' status effect.
It's an arbitrary brake-pumping for no reason except 'immersion'. It would stop the game to make players leave the cave they're in to rest or suffer penalties in combat.
If Larian wanted to add it as an option; cool. Make both sides happy. I could be cool with that. Maybe even make it permanently on in a Hardcore difficulty.
But I'd never turn it on, if it were toggleable, myself.
What about Role Play ?
Because this is what it's supposed to be...