They have their own ranks though don't they? Like some are Specialist, eitherway, it's a decent idea but maybe they have to gain xp from being on activy duty.
You can put Doffs on space duty, so maybe those which are listed there could appear on the bridge randomly as well as appear through the ship, it would give less of a generic feel to the Engineering deck and Crew deck, lol.
Also, those on ground duty could possibly be selected as away team backup? Like the tactical escort but only avalible in missions.
But during space/ground missions, while you might not call on them, they still gain xp which you don't see, then eventually you'll get a notice saying "... can be promoted to Bridge Officer" and the rareity of the Doff depends on how fast they level up.
That's adding more mechanics than what I believe you where suggesting though :p