Faced with a waiter or a person behind a counter, there's no way I'd order glass of a lime-and-raspberry half-sugar half-diet cola, for a number of reasons: I'm not going to bother looking through a menu to see what's available; it's not explicitly on the menu, and I don't know how the system behind the counter works, or how much extra might be charged for such an odd order; I don't want to be "That Guy".
If I want something half-way between a macchiato and a cappuccino, but with the coffee poured on top of the milk, then I'd rather do that by pressing buttons on a machine, than ask a server who relays it to a coffee wallah who then looks quizzically at the instructions and asks the server for clarification who then passes the question on to me...
This is just my dumb opinion, and I dont mind risking looking like that guy to share it.
Actually, I think that's something that would be relatively easily to automate. I've seen computerized ordering kiosks in European fast food restaurants. If you already have the robot, all you'd need to do is add a custom-item builder to the ordering interface. If the customer has a loyalty card or account, they could built it offline and save the item to their account for later retrieval.
Assembling a liquid product seems like it'd be much easier to automate than cooking or general cleaning tasks. Overall, though, your point still stands.