It would be the case, that the first auction ending, that you are bidding one, would have to be the priority item, that would stop bidding for other items, from the same seller, even if you prefer, say the third item ending, out of five items from the same seller.
In that case, by winning the first item, and having my shipping cost sunk in that item, then I would be willing to bid higher on that third item, I really want. I look at it as if part of that shipping charge is going towards the price of the item. Therefore, I can afford to pay more, when the shipping cost is divided up among multiple items. Other buyers, that do not have money sunk into shipping costs with the same seller, probably will not be willing to bid as high, because of the shipping cost. Thus giving me the advantage in winning the next item. Just my theory anyway.
Although, it may not be useful in every case, I believe that it would be a useful tool to users of this website.