Since motorcycle windshields are relatively soft material (ieolycarbonate), my guess is that a wiper is likely to rub grit into the windshield and scratch up the finish. Auto windshields, on the other hand, are made of glass (at least on the outer layer) which is much harder and more scratch resistant. But I am sure that someone somewhere has a windshield wiper setup available for a motorcycle.
The Japaneese export version of the GL1800 has a wiper. Think they may re required in Japan. There is an outfit called F4 making scratch resistant windshields with DOT certification for bikes, and likely you could adapt a wiper to it.