And preferences of making it easier on employees, or arguments that not following it could hurt business, fail almost universally. Customers' preferences don't work at all. (See all the airline "stewardess" cases from a few decades back)
BFOQ pretty much only succeeds when its an absolute physical requirement. Or when has some artistic/creative component - such as a character in a movie/play/commercial who has to be male or female. I don't know of any cases that tried a BFOQ defense on sexual orientation, though. Probably because sexual orientation isn't a protected characteristic under Federal law, at least yet.