Beautiful picture.
The amount of detail is wonderful and the concept itself is incredible.
In my opinion the eye-catching details and the impetuous shading which make it a really good picture at the same time make it a average wallpaper. Although in time I could get used to it, at first it would definitely be to distracting for a background.
You could also think about changing the transparency of the fog, e.g. more transparent in the higher parts and less in the lower, though I'm not sure of the outcome.
Still it's an impressive piece of art.