Hey! Thanks everyone for taking in consideration my suggestion and all the feedbacks!
Even if not eventually implemented, is pretty interesting to jot down ideas and share different solutions!
In general, I would say that the best solution must be easy to implement and develop into the game. It should work as an added nice detail, but not overhaul the established gameplay dynamic. Or, at least, that's not what I intended by proposing the concept.
So, for example, I feel like changing the whole resource-gathering dynamic by making it unlimited kinda push everything a bit too far from the purpose at hand.
To avoid too much confusion I think also that if we want to simulate a food supply system, is better to choose from one of the shared solutions, being either some effects on the food resource counter, or with some effect to singular unit's HP, but not a mix of both.
On one hand, I like the food trickle idea for being quite straightforward, with a clear cause-effect between unit movement and food consumption. Especially if this is supported by introducing the expenses in the GUI
On the other hand, I like also the vision proposed by Badosu! I haven't thought about RoN supply wagons, but sounds like the right model to follow for this game-mechanic. In this case, in my mind I was thinking about some standard "autonomy time" for the units when they leave your safe territory, and when this initial time finishes you start to have some slow effects on their HP (or maybe just the already mentioned "attrition damage", but at a very slow rate). No particular need to represent this visually, other than the hp line at some point slowly depleting. This should allow you to move your people freely anyway, and maybe do some very quick skirmishes and raid with the cavalry, but if you plan to start a proper campaign or sending your villagers far away to gather resources, you better claim some portion of territory or make sure your troops are supplied with either a wagon thing or some technologies to unlock.
Think about priests. You can be totally fine without, but is just nice to have a couple or more with your army to cover your back. Similar way, it shouldn't be a feature that cripple movements and gameplay, but you wanna take care of this if you deploy some big strategy.
In both cases, the goal should be to add a little realistic "nuance" to the battlefield, a small layer of complexity to consider strategically, and a deterrent for spawning massive armies and just flood the enemy without thinking. With this feature you should have some proportional food cost counter-balance to prevent that from happening too often.
If it goes too far beyond that, and if requires too much micromanaging then maybe is not a feature worth pursuing in my opinion, as the game is already rich and this should be only a "plus" on top of what's already there and works well Just my humble opinions as a random player just happened to pass by this forum! Obviously the last word then is to the devs or whomever wants to experiment with the concept, but again, is very cool to have the chance to share at least some ideas
Have a good day everyone!