Interesting concept think of a type of movie theme that you think hasn't been made yet.
Some ideas:
1. A Sci-Fi/History hybrid. Think Alien Invasion in Medieval Europe. (Similar to movies like War of the Worlds which adaptations have never made in its actual setting (Victorian England) from the books, outside of the musical)
2. A World War 1 or World War 2 movie from the perspective of black soldiers who fought alongside the allied troops (Love war movies, but its gotten to the point where they are all the same at this point, not that I mind, but there are still so many perspectives we have not seen)
3. A Baldur's Gate/Forgotten Realms movie. Because why the hell not :P