Yes, "small beer" or something with a minimal alcohol content seems very possible to have been what Joseph Smith would have been referring to with the "mild drinks", if not completely non-alcoholic. I don't know enough about historical beverages to say whether completely non-alcoholic drinks would have been around much.As far as barley drinks go, on my mission we were instructed to drink a common barley tea (a hot drink, frequently), in lieu of water, so I am aware of barley based drinks that exist, but I have been unable to find evidence of common beverages that would have been made by the people of that time and place other than "beer" and "small beer" (a beer with around 1% alcohol).
They could have produced it, but I'm not sure if they could have stored or transported it. Probably not, I think. I've never researched this, but I doubt that bottling technology was very advanced back then. They would have had no idea of germ theory, so they wouldn't have understood that completely sealing potable water from outside contaminants would keep it potable.And while I understand that alcohol may have been needed for preservative purposes, if distillation technology was there, why not just produce potable water?
God is unchanging, but people and societies change. Therefore I think it's reasonable that God's directions to us will be tailored to the society in which we live. That's a major issue I have with people (some born-again Christians, for example) who feel that the Bible is the sole and complete word of God--just to take one quick example, Paul specifically tells the people (Corinthians, I think) not to let women speak in church. Well, that may have been appropriate for their society, but I don't believe that's what God wants for our society. So, to me, continuing revelation makes perfect sense, even if it leads to one group of people receiving slightly different commandments than another group. Sure, the biggies will stay the same--love your neighbor will never go away :-)--but things like modifying the WoW to now be a complete prohibition on alcohol/coffee/tea don't bother me too much. And I think someone else has already brought up drugs like heroin & LSD which didn't even exist in Joseph Smith's time.Lastly, and this is my biggest hangup, is that all my life I have been taught that God is unchanging - the same yesterday, today, and forever. But the WoW doesn't reflect this. I understand that as mankind and society expand and evolve, some things need to accommodate. The Law of Moses, for example. But to me, the WoW seems like it should be straight forward, and that there is no need for it to apply differently to various generations of the church. From the get go, God could say "Don't consume this, and this, and this..." But perhaps I'm looking at this too simplistically.