personally i think it would be an interesting mechanic, but it could instead of being used as a main function of metal plates, instead be used as a last resort by the crew. so say your crew runs out of supplies. they then start to cannibalize the cargo holds contents to fill in the gaps that makes, so to keep CR up etc they would start to eat your metal, food, etc. albeit at an quick rate until you can get proper supplies. though not so quick as 10 to one, thats just silly. i would say 200% of your supply consumption value, obviously not affected by skill modifiers.
Additionally you could limit the max CR a ship could recieve my saying, you can only get 10% CR per item the fleet can consume from storage. So only one type of commodity say metal you would only be able to get 10% CR per ship this way. But if you had metal and food then you could get up to 20%CR. I would also limit the types of cargo that can be consum d for CR to stuff that can make some logical sense. Like metal, food, volatiles, luxury goods. Organics. Harvested and cloned organs. (Though obviously those last 3 would be pretty low on what most people would want to eat, in an emergency faced with death, we would likely eat it. ) I would further limit max CR with this method of emergency rationing to 50%CR max.