The reason they've never done this in their previous 18 years of existence is because of the enormous army of bots. The moment voting opens for who will mod a subreddit is the moment those countless bots wake up and vote for whoever controls them. Then you're not democratising power; you're consolidating it. And before you start down the path of validating the identity of every user, consider the astronomical costs and legal and ethical implications.
I'm happy to make this bold prediction: they're never going to have democratic voting for subreddits. Huffman is only using words like "democratic" because he wants to break the strike. If this all settles down again those head mods (whoever they be) will remain little kings.