I think there will definitely be a tiefling as a companion. Probably the one from Avernus that the Tyr group wanted us to decapitate. She has the worm and a story of wanting to escape from her captors. I know she brushed off the chance to join but I bet we bump into her later.
You're absolutely correct! Dataminers have found that she is an upcoming companion, and she's the only one of the three they've found with recorded voice lines right now. she seems cool.
