I think I may have figured out a clue as to what exactly the demon beasts are. I felt that they were df users, but something just didn't feel right. They don't seem to be able to speak, they were referred to as monsters who treat humans as trash, implying that they are not human. Anyway, look at their hands. http://www.onemanga.com/One_Piece/533/10-11/
Then, look at monster point chopper's hands. http://www.onemanga.com/One_Piece/411/04/
They look the same. That's not how regular zoan hands look. I think vegapunk is behind this. I believe vegapunk has found a way to manifest the devil fruit's own form without a host. Well, at least for zoans. That or he's come up with something similar to chopper's rumble balls with a longer lasting, not so giant effect.
I'm wondering if when the minotaur falls into the blood lake, we'll just see a df floating by. In other words, it will revert the minotaur back to it's sealed form, which is the fruit.