What is Going to Happen in Legends of Tomorrow Season 4?

What was with the clip at the end of episode 18 (the finally) of DC's Legend's of Tomorrow. Constantine just strolls up to the Legend's and dumps a dragon/lizard looking head that had been cut off something. Then he says "Who's brilliant idea was it to release a time demon". So after that it got me thinking what could they lead on with that little snippet into season four and then I thought that they could link the Legend's to the Justice League Dark. If you don't know what that is it is just a small portion of the Justice league that more works against stopping things related to magic and demons. So I think that would be a cool addition just for even a few episodes of Legend's of Tomorrow season 4.