I really don't understand the argument here. The game is not designed to simulate whether each country could feed its entire population adequately, it is designed to simulate whether countries could adequately conduct war operations during the WWII era. In game terms, i.e. the engine as we currently see it implemented, how is food *NOT* adequately simulated by the manpower, supply, and consumer goods metrics?
The manpower limit is the manpower available for the armed forces AFTER accounting for food/industrial production; i.e. we do not get to choose to draft EVERY person out of the fields/factories and put them on the front lines.
Supply is many things, such as ammo and clothing, but in my mind it is also food/water and other necessities, as well as the means of storing/distributing them. The IC which we control in-game produces this -- we already have a metric for controlling it. Yes it is abstracted, but I think reasonably so -- I do not particularly want to have to worry about planting/harvesting wheat in Iowa, meat in Texas and dairy in Wisconsin, processing it in Chicago, and then moving it overland to ship it to troops in the South Pacific.
Consumer goods are many things, but to me this abstracts just how many sacrifices you are asking the civilian population to make in order to run your war machine. Too many sacrifices = too few consumer goods (i.e., you allocate IC from CG to something else) => unhappy citizens (i.e. dissent) => lower IC. Yes again this is abstracted, and perhaps it could be modded/tweaked, but how does this dynamic not get at whether the civilian population is affected by the war?
I *DO* agree that food is the basis of all economic/industrial/war activities; without it, you cannot effectively conduct a war. But I think the basics of this are already modeled -- Japan gets much of its IC from their mainland holdings, so if it loses these then its war effort is largely screwed; same for UK losing India. Or, at least, these things are modded well in HPP. However, I would be in favor of some kind of agri-bonus for holding key areas such as the Ukraine (as well as favoring some kind of scorched-earth method of denying this benefit to the enemy). I just don't see a reason to rewrite the engine to cover something which, while abstracted, already seems to be covered in game-terms.