I think it would be much easier to just reduce the amount of food we can find drastically with almost the same effect. If you don't have a lot of food in the first place, you will also think twice about resting. No offense, but I think the approach you are suggesting is just too complicated for a videogame where the developers are already struggling to not overwhelm new players who don't know DnD 5e with all the rules and mechanics.
Also I am not a fan of saying goodbye to NPCs that have a rich story of their own just because 'they cost me food'. I mean sure, I almost never actually use Gale for example, but I like having him around in my camp anyway because I like my camp to feel alive and I like interacting with him and finding out about his story, even if I don't run around with him all the time.
It is a bit different than simply limiting food. It's about mentality. I acquire 300 food. I'm feeling like I could rest a lot. First LR, spends 60. Wait. Now I'm at 240. Dang! Now I'm doing the math. I get 6 more. That's it. What if I don't find more food? Find another 50. Oh. Okay. I'm probably okay. I'm not stressing now, but in the back of my mind I'm thinking what if I hit a dry spell? SR costs WAY less. Maybe I should use that more.
Versus - I only find 40. Each LR is 40. I get 1 rest. Oh dang! Now I'm stressing for real about a game. I find 40 more. Okay. Still stressing but not as much. Dang! I need to LR. I use 40. I only have 40 left. I MIGHT or might not find more. I have no clue. Oh! Bad luck. RNG on last battle was BAD. I'm so screwed! I have to use my last 40!
And again, this system isn't FORCING you to get rid of party members. The safety net is vendors. Spend a bit more, keep everyone in camp. Maybe costs 30 gp pet LR to keep 9 party members with a party of 4 multiplayer session. Not exactly breaking the bank. But, it gives you the strategic option to boot them if they aren't worth it to you.
The concept is like this: You have 1200 euros to spend. Your bills are 1100. You have 100 left over. You could either spend 20 on some sort of subscription for some channel you really like, or you could spend the whole 100 on going out with friends and such.
It's the same thing I'm suggesting. You have 100 gp to spend. How much is having all those party members at camp worth it to you? You could either spend that 100 on new weapons and equipment, or you could spend maybe 30 of it on a camp supply pack because you didn't find enough food in the world to support the whole 60 camp supply cost - or you long rested too much between fights and you're running just a bit short of camping supplies.
In other words, the only time it would be an issue where you'd feel like you need to maybe think about cutting party members is IF you both long rest a lot and you have a lot of party-member potential characters at camp. Otherwise, with the amount of food Larian already has in game for you to find, you'd probably be just fine never spending a single gp buying camp supplies.
The vendor is ONLY a safety net where you'd need to spend more, and the number of camp members would ONLY be an issue if you long rest a lot. And then, even then, the cost of buying food should be cheap enough that you never get soft locked in the game or have to start selling really cool items just to long rest.
Again, the point is to discourage one rest over another, but to provide value for both, and it ISN'T to try to force players to stress over food or resting mechanics. I REALLY don't want to create a system where people are stressing over resting. That's completely against the point.
