well, since i do occasionally run a drive-thru at work (although not at mcdonalds), i think this could be a pretty decent idea. i don't know how they do it at mcdonalds, but if you're running drive-thru at my place, then that means you take the order, dress any sandwiches they ordered, put down your own fries (and whatever else is getting fried), cash out the customer, and finally give the customer their order.
i've gotten pretty good at it, considering we have to do so much at one time (my current average is 198 seconds, or 3 min & 18 seconds per car). this kind of idea would make it easier on whoever runs drive thru up where i work because it eliminates the hassle of trying to take orders while your trying to fix someone else's food. i also like the idea of taking the picture of the car so that you know for sure that you can match up the person's order with the car, in case someone drives off.
thats why i say don't laugh at an idea if your not entirely sure about the situation to begin with.