I've done this in stellarium to some degree but i am still not very happy with it because I still can't quite get an accurate estimate without a tremendous amount of manual work, so someone actually actively working on this would be amazing.
As I said in another comment, a true killer feature would be to image my yard, with all the obstacles blocking the sky, and intersecting the available sky space with the trajectories of those objects, and use that info to actually tell me what I can image.
A widget version would be nice!