I have to say, although I don't have an issue with NPC Crewmen per se, I just don't get it. What advantage would you get from an NPC sitting next to you, when you can control any ship as an individual? Unless there is an expectation that including NPC crew members would increase your in-game abilities, or power. I can't get behind automating ship functions via crew, especially an Auto-Pilot. It would be the worst thing possible to create an NPC that can distribute my pips, or use my weapons as in Multi-crew.
Whilst I'm an advocate of an NPC system with static buffs (and maluses) to ship systems, based on crew skills and personality, rather than having them act as autopilot, or actively controlling pips or whatever. I think even such a 'simple' system would help flesh out the single-player game. That said, I think it's on a deeper, psychological level that NPC crew work for me - and sorry, I'm going to invoke the dreaded 'I' word... <drum roll> IMMERSION!
The big ships just feel 'wrong' and empty at present. I've grown up with Elite lore going on about navigators, gunners, co-pilots etc. in pretty much anything bigger than, and including, the Cobra. I've grown up with the buying a big ship in FFE or Frontier, then having to find and interview another 5 (or whatever) able bodies via the bulletin board, before I could fly the thing. Even if I couldn't see them, and they didn't impact on gameplay (once in place, they killed gameplay stone dead if the bulletin board didn't generate any crew adverts for that day), it felt like an added layer of depth to the ships.
And now, of course, we have the possibility for 3D proc. gen. avatars, to again help with the 'I-word'. I just want to look over my shoulder in the 'Conda, see others, and have the feeling that I'm in command of a big(ish) hunk of metal. Yeah - there'd be issues, even with purely cosmetic NPC crew, e.g. what happens to them for multicrew? Do NPC crewed ships simply not get the option for MC? How are crew deaths and survivability handled? etc. But I think these could be thrashed out.