I quite like your ideas on food, Walltar. Having some small debuffs if you're hungry, like being a little bit weaker (like for lifting stuff and how fast you swing a sword and that) or slower or something (stuff that is barely noticable, really) would be preferable to just dying if you don't get enough to eat. it would be good for the folks wanting realism, and not be too big a deal for those who don't.
Although, not entirely sure what you meant by food being eaten passively, but I'm guessing you mean it's eaten automatically if you get hungry and it's in your inventory? I don't care for that, especially if different foods have different bonuses. being able to choose what you eat is essential.
I also think it'd be neat if you have to sit down and relax somewhere to actually eat something, and show an animation of you doing so (nothing more than like, 10 or 15 seconds, though). Well, maybe you shouldn't HAVE to find somewhere cosy to eat, you could easily take a few seconds to wolf something down in some dark corner of the underworld, or some forest or something, as long as you're in a fairly safe location.
One thing that would have to be done if hunger is implemented is have it happen very gradually, where it's not at all noticable for quite some time until you can see you're having some small difficulties (only up to a certain point though, where even when you're starved, you're still capabable of doing stuff fairly well). A system where you're running along and all of a sudden, you start walking more slowly (hence indicating you've gone up a hunger level, or something) would be immersion breaking, for one, and it would realy annoy folks who aren't for realism in this game, as the game is essentially telling them "you have to go eat now". It should be a case of the player deciding they should eat some of that bread and cheese they brought with them, so that they stay at the top of their game, you know? Not HAVING to eat because it means you'll be really noticably weaker otherwise. I know it seems like the same thing, but that small difference would make any hunger effects seem much more different, in my opinion.
Really, most realism type things (being affected by weather, hunger, thirst, being overencumbered) should be a bit like that. Something that happens gradually, not really noticable for a while, which gives the player the choice to remediate it if they so desire (which means NOT killing the player or giving them really really noticible, immediate debuffs for not fixing it). It should be something that the player can just shrug off if they have to, and keep going, or they can do something about it and alleviate the problem.
For instance, I liked the "limited" inventory system wherein you have a bag or something you carry around and you put your stuff in there, but, using the game's physics, carrying lots of stuff around would make you unbalanced and heavy and slow.
As for questions like "how are you going to fit a suit of armor in the bag?" keep in mind that metal armors are just seperate pieces of metal. You could easily just fit each piece in a bag a bit more compactly, and the "loot" bag I imagined was like a big sack, which you carry with you fairly easily (slung over your shoulder like a cartoon robber might carry a bag of swag), which you would quickly put down on the ground if you fear an enemy might be close or if you need to do something. Pack mules and horses could play a part in this too.
Of course, another approach to these things would be to have them be optional. As in, have a "survivalist" difficulty option, so that people who just want to go adventure and explore without worrying about inventory space, food and water, etc. can go do so, and those that really like planning ahead and having the worry of finding food to eat and wondering what to carry with them and what to leave behind can do all of those things.
Just my two cents. Okay, rant over. Sheesh, I talk a lot when I want to, huh?