As above:
I've been using a theme I made for a while, but don't want to release it yet. It isn't that different to the unofficial ones. It's just a few color settings.
But there are some things we want to add before we release an "official" dark theme. We're also looking at supporting some extra things like dark titlebars, but the API is still undocumented and, worse, keeps changing between Windows 10 updates and breaking things, so we're still waiting to see if that ever becomes stable. (Microsoft are really screwing up here, to be honest.)