I wouldn't be surprised if one of our companions is an android. Maybe working for either the Institute to chase down runners, or part of the Railroad and helping androids escape to freedom.
I know nothing more than surface information has been released, but I think it's very possible we may have an android companion. Pete Hines did stressed in an interview that romances were only available for "human" companions. I know we have Dogmeat and Codsworth in two of those slots, but humanoid robot seems to fit well being where we are.
I personally think The Institute will be a big part of the main story and that they well may have had something to do with the events of Vault 111, and directly impacting the life of the Sole Survivor.
I most definitely think the Railroad will be a full fledged faction and that the PC will have to choose between being a Deckard or Harriet Tubman-type.