The lifespan of the average male companion in NuWho is incredibly short. Adam barely had time to unpack. The closest thing Jack got to an alien civilisation during his companion days was Wales. Mickey got little more than a parade of slightly different robots and Rory's tenure in the land of the living was so sporadic it became an in-joke. With the exception of Captain Jack (arguably), all these transient TARDIS tenants have one thing in common - they were romantically linked to the female companion. There was little doubt in anyone's mind that the writer's only purpose for the token male companion was as a springboard to develop the female companion whose usefulness would end if she decided to leave, assuming he hadn't already been ditched. I would like to see a new male character be introduced midway through the series (not at the beginning so that the new dynamic between the Doctor and Clara has time to settle) who joins the TARDIS crew because he impresses the Doctor enough to be invited along. Then he should stay on the show until either the actor decides to leave or the writers decide that he's reached the end of his arc and becomes superfluous. He should interact with and have some sort of platonic relationship with Clara, but not a romantic one, not a submissive one for comic-relief and should not be dependent on her to keep his TARDIS key.
