By that logic, you would only get weak units produced.
Say you have a goblin that costs 10 metal and an orc that costs 25 metal. You want a nice mix of both so you insert goblin,orc,goblin,orc,orc in the queue. The result should be 2 goblins at every 3 orcs, but with the above system there would only be goblins when your stocks are below 25 (and will never reach 25 at this rate, since it will autoconsume for goblins).
You can extrapolate the example on a larger scale, including very expensive researches that will never get done because of the queued cheaper units.
The basic fault is that rotating the queue by resource availability kind of negates the idea of a queue: an order of items.