@Stabbey This could be an interesting solution despite being a disguised time constraint. There is one major problem and one major benefit I see here.
Let's see how this could work :
In this case we want to have a fatigue treshhold giving you exhaustion points, up to 5. At 5 we go to sleep.
We have a cooldown that you cannot bypass (for now) for long rests. Long rests being the only way to get back your spells as a mage/wizard.
Short rests give us back our hp + special actions.
It brings us to the logic of D&D when you won't long rest twice in a row cause only 2 hours elapsed in your role play. It also forces you to use your spells carefully and to scout before engaging in a fight. You cannot end up in a fight not knowing what awaits you later on. It forces you to use more mechanics from D&D, including certain spells like invisibility( even if it already has an application right now).
Sooner or later you will deplete all your spells. Let's take the goblin camp as an example.
You cleared the gate and sneaked inside. You executed everyone inside. Outside you have 18 enemies awaiting you. You already killed around 20 of them and you're low level so you're in need of replenishing your spells. You have 3 fatigue points(for now we don't know how they are generated).
At this point we are down to short rest and let's go. This encounter is doable with cantrips only for mage and you still have your melee/archer characters that can do the damage. After the fight we have 5 fatigue points. Long rest, and let's go.
The major issue I see here is -> Sooner or later you might end up against the wall with no possible solution.
If you replace the 18 super simple to kill goblins with a boss where your wizard is actually required there is nothing you can do to fight the boss in question. Or rather your mage will be borderline useless during that fight. That will be super difficult all of sudden and might become frustrating. Unless you balance the game around cantrips and melee characters.
You can eventually leave and come back for him later. That would make sense, you're not in power to kill who you want when you want at your level. And that's the wall I'm speaking off. In D&D it would make sense story wise to leave this fight, do something else and you're still playing.
In a PC game you're loosing content. If you have to skip some fights or have serious issues during them because " you're can't rest yet" that would ( based on the current form of BG3) become an issue.
Not sure what you think 'bout it? I love the aspect of resource management in games, I like how it was implemented in hoi4,wasteland 3 or XCOM 2 while it was insaley frustrating in case of Pillars of eternity 1. Those examples I provided are for the most part not even RPG games but it doesn't matter. But they approached the same subject and they were praised for it. Apart from POE1. In bg2 it was ignorable.
I think the solution would be not to limit how often you can replenish your ressources to 100% but where you can do it. I think the best way would be to provide "camping kits" exactly like in POE1 but give you like 5 of them. More than enough to clear one of the zones of the map. After this time you could come back to the town and buy more of them.
Now you made the player come back to the town and...what for exactly? There should be some kind of gameplay there. In wasteland you had your base to manage, upgrades to make etc. In case of BG3 you have items to sell, others to identify( hopefully!). So it would make sense to some extent. But then you're effectively making an illusion of resource management while in reality you're never in the risk of running low on anything. In wasteland it worked because you were buying ammo type for each gun , upgrading them etc. If it sums up to " buy this item 5 times" it will be pointless.
Yes, i have no solution for this. Yours is the closest one to become a good idea BUT we would need to find something for the " wall" i mentioned.
I see that you associate the system with PoE1. You know how annoying and pointless this system was at times. This was especially noticeable when you tried to clear the dungeons under the castle.
Rest-restricting items make no sense in a game where you can return at any time.
In the game we have a fast travel system which, even if it is limited from one point to another, will practically invalidate the possession of items.
In that case, we might as well remove them.