+1
You said it very well that there are two possible outcomes. I am finding so far that #2 is mostly true (you do not need most slots for most fights, so with constant long resting you can steamroll most encounters).
I wonder if it would be possible to add an actual day/night cycle to the game. In 5e you gain the benefits of a long rest only once every 24 hours. This prevents the problem of trying to constantly long rest in a dungeon etc. I imagine this would be borderline impossible to implement in a reasonable way but mentioning it as another consideration.
Another possibility that would probably fall under the idea of resources is that you must earn a certain amount of XP between long rests. The amount would scale based on your level. I could see this causing potential issues where you could get stuck with too few resources but maybe a hard save and a "reset to last long rest" option could help avoid any major game-ending / TPK issues.
