20-Year Prospect
People love coffee and keep finding new things to do with it. Another coffee shop pops up every couple of days. There is such a market for coffee that there can be seven shops on the same block...which all do really well. Sometimes the same shop opens two locations across the street from each other. The job market is just going to keep growing, as far as the Bureau of Labor and Statistics can tell, so barista jobs are pretty safe (source).
There's always the possibility that in the distant future we may be served by robots, but that's not likely any time in the next twenty years. Coffee orders can get pretty complicated, and for now, it takes an actual human to get them done.
Barring a scientist finding out that there is gluten in coffee, then this job isn't likely to go anywhere.