Maybe it could be a new song. But, I don't think so. My opinion is that because of the story of Medusa looking at the mirror, which is killing her, we could have the song "Dream Of Mirrors" replacing "Death Of The Celts". Or, "Deja-Vu" (which is a kind of mirroring in the future). Or another song talking about snakes and serpents ("Be Quick Or Be Dead", "Revelations"). Everything is possible. But, for now, I don't know it's about a brand new song. Unless they've secretly recorded an album (when and where ?) that will be released for band's 50th anniversary next year...