Not sure the companions are really as marketable as the Doctor and the monsters. When you look at how many companion figures there are (with the exception of show runners Sarah Jane and Captain Jack), there really is not that much.
BTW I wonder if there will be more season 5 figures? I'm suprised a Silurian warrior was not included in the first set, and there's potential for a Cybermen variant (Not sure how it would work though). Plus the Centurion from the Fires of Pompeii set should be easy enough to use for an Auton (or Rory). Plus there's the Doctor in the wedding suit/hat.