Don't take this post as a "for" or "against" the idea.
However, NPC factions can be joined by any player at any time. Other members of the NPC faction cannot remove a player, either. There is no way to ensure you won't get trolled in one or all of the myriad ways this could be a bad thing. In fact, I can guarantee it. Also a concern (though likely a lesser one) would be that anyone can join an NPC faction and loot the TC locker. I wouldn't care, others probably wouldn't care, but some would.
This all assumes changes to only what has been suggested. Other issues would become apparent after implementation I'm sure.
That being said, NPC factions having some rewarding value to membership can only be a good thing, so I can support anything going in that direction even if it doesn't immediately benefit me.