Any efficiencies you are seeing will be refactored and stretched out as any business cannot afford to carry fat if they want maximum profit and competitive edge (price).
This whole inconvenience of a friend going to the bathroom is an incredibly weak argument for foregoing the tradition and ceremony of interacting with a person who will provide you with a meal. If you want to live in a McWorld where every step of your dining experience is as sterile, efficient, and touch free as possible then I am sad for you. That's not what a meal with friends and family means to me, it's not just about eating for sustenance.
Why do you draw the line at taking payment?
We went out recently to a place where we ordered with our phones and had a great time. It was simple and painless, orders were served quickly and it didn’t matter that the only thing I ever said to staff was ”thanks” - I focused on my people instead.