You really are'nt going to let this theory go, are you? Spoiler I'm pretty sure Book's just an hitherto unknown alien who, in the grand star trek tradition, happens to just look like a Human. That or he's a waterbender. As for the wormhole thing - come to think of it that maybe how ships travel now; artificial wormholes (perhaps the Trill character won't be a Dax, but rather a carrier of the Kahn symbiont instead?) There were actually two Trill in the s1 finale of Disco - one at the Orion brothel/carabet and anouther (who I'd like to imagine is Emony) getting a tattoo.