Computerized bartenders are always fun, but there is always the challenge of keeping them clean enough. And will the Ardunio chip be available as a replacement part in six months? It is an interesting project, but I wonder about how much has been done as far as verification that all of the valves are food service rated. Alcohol, fruit juices, and sugar, can be hard on a lot of materials. Also, has the system been checked for immunity to inebriated operators?
It sounds like a fun hobby projects, but as you mentioned, WKetel, a lot of sanitation concerns. One of the niceties about self-used hobby projects is that you don't have to worry about such details, but if you're going to promote and/or sell the device or design, it becomes important to either build the system to mitigate those concerns or make sure they are clearly documented.
If you're going to sell it, you really have to address the concerns. If you're just going to present it as an open source design, I think you can get away with just documenting and suggesting ways to take care of it. Unfortunately, depending on the common sense of the user isn't enough.
I would certainly need a similar machine that could make single cup coffee pods at mornings, sometimes I get too late and don`t have enough time to prepare the coffee. Making such a machine is not a big problem for a skilled engineer specialized in Arduino prototyping platform, I will ask my brother if he can make it and if so I will give him all the materials he needs.