I think that the concept of instituting a six-month prohibition underestimates a few things. First, the (lack of) speed of the government. Unless they were able to pass the law, institute enforcement, and destroy existing stock in a matter of days, most people would merely stockpile. For me at least, if I had a month's notice, I could easily buy enough beer and wine to last me 6 months, and keep it in my basement.
The criminal organizations who would circumvent these laws are much more agile than they were 80 years ago. Like every business (and they are a business) they've modernized and streamlined operations, and adding another product line to their existing ones would not be a large burden for them.
Finally, you mentioned that the "the quality of American alcohol has never recovered." An ordinance like this would guarantee that it never could. It hasn't been until recently that small brewers and wineries could begin to compete with the big names. A large portion of this is due to the fact that having access to large varieties of breweries and wineries, so they are able to develop their pallates and education to the point that they know why the beer from AB tastes like crap. If this were instituted, AB would be able to survive on sales in other countries, and their existing capital. However, small breweries and wineries would be destroyed.
While I can see that many people would benefit from drinking less (I work in an industry where substance abuse is one of the biggest issues.) I don't think prohibition would solve the problem in the least. The portion of the population that drinks because they appreciate a good beer or wine would largely lose access to that, while the portion of the population that abuses alcohol would, at most get a temporary break, and after the prohibition ended, they would return to their habits.