Another idea I had was that they could limit Long Rest by having characters refuse to do it unless there is a significant need. Basically, instead of them saying they are tired for dialogue triggers, they say they aren't tired when you try to Long Rest unless you meet the prerequisites.
What would be required for a Long Rest is the following:
1. Short rests all used up.
2. HP less than half collectively. So if all party members have a total of 80 HP and together they have less than 40.
3. 1 or more characters with no more spell slots and/or special ability slots
4. Not in a dangerous location like Hag's lair or gobbo base
5. 1 Food item per character in the camp.
6. 1 Drink item per character in the camp.
Doesn't have to be this exactly, but thinking something like this. Than restrict short rests a bit too. Short rests would require:
1. HP less than half collectively. So if all party members have a total of 80 HP and together they have less than 40.
2. 1 or more characters who have used 1 or more spell slots or special ability slots
3. In a safe location where no enemies could wander about and find them. So Larian would need to create Short Rest Zones and limit how many there are.
4. 1 Food or drink item per character in party, so probably 4.
Short rests would then be used to recover HP, 1 Spell Slot for Mage and maybe even Cleric, and Superiority Dice, etc. Something like that.
This I greatly prefer. though i think shortrests shouldn't be restricted too much, even in tabletop they are meant to be used freely. I think they should just depend on how many "hitdie" a caster could have, so level. So a level 1 party can only shortrest once and a level 4 party could do it four times. Shortresting in quick succession only means they heal more cause most characters can only take advantage of X on Shortrest once or it falls off on shortrest. Just keep things as they work in 5e for shortresting and give some limit to longresting like how you mentioned needing a resource and the characters to be tired. Also long resting needing food actually is in line with 5e as characters are supposed to eat rations to avoid exhaustion.