I was so hopeful for it this year, and would gladly welcome it, but I'm still of the belief it just doesn't make sense for Apple. Dark mode won't serve a real purpose, both from a software and hardware point, until they move to AMOLED displays in 2017.
I think they are in the very early stages of development for it, but they will, and should, spend the next year refining it to ensure a great, fully functioning rollout.