It would be feasible, with current technology, to completely automate fast food assembly.
Grocery stores already have cashierless checkout lines.
It wouldn’t be a huge jump for McDonalds to completely eliminate nearly the entire staff of a retail location and replace them with machines.
There’d probably be fewer order mistakes too...
I use the one in our local store all the time. They offer a scanner to use on your shopping trip so you can scan stuff as you buy it. I LOVE it because I bring several bags with me, scan the items, and load them as I go through the store. When I get to the checkout, I 'scan' the scanner, scan my Shopper's card, run my credit card through to pay, and wait for the receipt to print. Then I just walk out and load my groceries in the car, because they're ready to go!