Yo, 5x food consumption isn't going to do a damned thing to a player's ability to carry enough food to roam the continent at will.
If you don't want to bother clicking the pic, it shows a party of 210 men carrying over three and a half
years (in-game) worth of food, for a total speed penalty of -0.12.
Also, it isn't hard to get more food in the enemy interior currently. Just go to an enemy village and buy it. It will be way more expensive because an extra trade penalty is applied during wartime but food is so cheap that doubling the price (or tripling, or whatever the penalty is) doesn't matter much. Whatever you lose in denars to the trade penalty is going to be a rounding error compared to the loot you get after a successful siege.
Finally, the AI can already barely manage its own food for some reason, so you'd need to completely exempt non-player armies and parties from this system or else the No.1 winning move will simply be following behind a (much slower) enemy army until all its men starve, then swoop in for a free win once they are down to zero available troops.