Why not just enforce long adventuring days to make casters ration their spells?
I think for DND what they ought to move towards is less of a specific adventuring day, and more just an enforced importance of time.
This is a thread in game design that Ive been pretty obsessed with ever since my intro to AngryGMs Tension pool illuminated the critical benefits of time actually mattering.
If time matters, meaning hour by hour and minute minute all time is tracked and meaningfully experienced, then you in turn recieve a game thats more immersive and easier to run to boot.
The tension pool accomplishes this objective because each die that gets added, or removed, from the pool represents a visceral experience of time thats directly correspondent to the players choices, and the consequences of time always advancing in the end are thus also viscerally experienced, and the players are able to feel how their choices impact their futures.
The riskier they play the more likely their adventuring becomes complicated by some unforeseen happenstance, and careful play in turn directly influences this chance, but also induces the, relative to real world time, much quicker passage of time if being careful ends up in them making time consuming actions.
Its a delicate line to balance, and the players directly engaging with this balance, metagaming if you will, is what gets us the desired immersive effects. They won't be thinking about how to game the tension pool, they'll be thinking about how their character will actually act in accordance with how they want to play and what they want out of the adventure.
And in turn, because the introduction of complications, whether it be more atmosphere or even additional random encounters, is effectively shared between the players and the GM, this makes the game considerably easier to run, with little negotiation or contrivance.
So to bring this back to the topic at hand, under the tension pool running an adventuring day that can adequately tax casters becomes easier because time simply must march forward, and so to rest comes with a meaningful undesired effect that players have to weigh against their desire to be at top fighting shape.
The DM does not need to arbitrarily spring a goblin raid the moment the players rest, and instead all faith can be turnt over to the dice. Sometimes resting in a dungeon may not result in some terrible thing happening. Other times, they realize they just slept in the middle of a Dragon's outhouse.
