Mobile skin is just a basic skin that takes away all the images and stuff and is not much more than text only. You can have onyx darker for mobile - just tell it go to to the full site at the bottom, then select the skin. Obviously, it won't be optimised for mobile then.
We don't really have anyone on the team who does skins bar Lunny messing around when he's bored, so I can't really say for sure that we have more on the way. Maybe at some point.
