They are planning to create Four/Adric audios - I think there is already a published short story from years back in the Traken/Logopolis gap.


At the end of State of Decay, the Doctor is telling Adric in no uncertain terms that he will be returned to the Starliner, but by Warrior's Gate, they seem like old mates. So there are other planets in E-Space, just from evidence in the TV show.