I think it invitable that The Traveler will not be fully explained. After all, they were hoping for more than just six episodes to wrap everything up.
Perhaps, but they had advance notice (the writers did) before even starting this last season. He may not need to be explained in detail if he is one of the characters already mentioned in the show (Sam, her son?). The Traveler has a time machine built into his body so he can travel at will (according to the Continuum Wiki). It could even be Alec's brother. We will see.
This show has been a bright spot in my viewing, and it will be missed.