This is a good change. Long Rests needed some kind of limiting factor. I also feel that if they should make it togglable it should be tied to difficulty. After all, is Hard really hard if you can just spam long rests infinitely? Meanwhile anyone playing on Easy isn't looking for a struggle for survival in the face of overwhelming odds. They just want to experience the story.
This is also a system they can build on though. Druids should be able to use goodberry to contribute to your food reserves for the evening if they still have a slot left over. Rangers and people with the Outlander background should be able to forage for food or go hunting when at the camp to give you more free reserves than usual. Things that can make classes more meaningful toward the resource management side of the game.
I'd also like not having enough food for a long rest to be reflected in the dialogue. Just little side comments your party makes like "I am so hungry..." or "I guess we won't be having breakfast either..."
If you skip multiple days you might even start taking a penalty to your party's opinion of you. Nobody likes going without food after all.
I made a post about this on the Discord feedback page, but I'll post my concern here as well.
Restricting the Long Rest system is good. It is a necessary evil. However, unless they are very careful, the system could result in a softlocked save state. If you require a resource to be consumed in order for your player to heal or regain expended abilities, you run the risk of that player running out in the middle of a long expedition. If you are lost in a dungeon and you don't have enough supplies to fight your way back out, and you saved recently, you are SOL.
I don't think there's a risk of this here. So far you can walk away from just about any encounter and make your way back to town if you need to, and there are so many ways to resolve an encounter that even if you somehow couldn't get food for a long rest you could likely find some way to resolve the fight without being at 100% anyway. Barrelmancy, shove them off a bridge, hit them with your shoe, etc.
