Delivery can scale if you get people to order in groups and have a minimum group size or something.
Actually having high quality fresh ingredients is a much bigger challenge. Look at Subway. They always have tomatoes but they're rarely good tomatoes. Even Chipotle can have very substandard pico or guacamole and that's basically their only really fresh ingredients (save lettuce).
All the other big restaurant chains use little to no truly fresh ingredients and for a good reason. It's a legitimate problem with few great solutions at scale.
That's part of why the local/seasonal food movement has taken off; restaurants can't deliver on a perfectly consistent and great menu year-round. But once you introduce the idea of local and seasonal then their hands are no longer tied and you can alter the menu at will. People might complain if they show up for a particular meal and can't order it, but ostensibly they knew that was a risk if the restaurant made this clear.
Given that you record preferences and emphasize the "surprise" aspect you might be able to scale appropriately.
But you may still find it's difficult to find any good ingredients at certain times of the year and have problems keeping the rotation from week to week large enough to keep customers happy.
