I think the best argument would be aesthetics. When grading beer on this site, most people include the appearance of the beer. It can easily be said that most people like to see what they are drinking, especially the crowd of people who take the time to pour their beer into funny shaped glasses. So I guess that answers why it hasn't really been done. But there could definitely be a market and crowd for this. Also, reading this thread has got me really interested in elaborately decorated ceramic steins.