In Italy (Gardaland, Milabilandia) and in the Netherland ( Efteling ) I've seen plenty of vending machines selling drinks, along queues. Not sure it's a good idea to open an actual shop in there, tho. Few pros, lots of cons. I tried buying a drink while queuing, I managed but it was... acrobatic, xpecially if the queue is well made (it's fast).