Whatever happened to the mechanical crewmembers that were proposed in the DDF? IIRC these were single-role robots that would add bonus functionality (but not as much as a human crewmember) and could be stored as cargo when not required. I'd like to see this idea revisited if we're not going to get fully fledged human NPC crew. It would even solve, to some degree, the voice acting problem since all robot voices could be synthesised.
They were all wiped out, in the Brookes Jihad.