The spent barley makes a fine pig food. Make it a portion of their ration, not the whole thing. If their poop starts looking like the incoming grain then back off on it. I would also suggest feeding veggies and pasture with it. Ease them into it. See how they do. We feed some, I would love to have more.
This is an interesting concept. It would be interesting since many things are flavored or marinated in something with a beer, or some type of liquor base. This would get a jump on that. Maybe a new market?