A couple weeks ago I was doing some research for an upcoming photoshoot with a pretty girl and a motorcycle. I knew the shoot would be in the evening so I did a search for "girl sexy sunset motorcyle". Much to my surprise, there were no silhouettes of girl with a motorcyle.
Similar thing, a couple month ago when doing a maternity shoot, I thought it would just be fun to do a "maternity water break" shot. I think this is the only "my water broke" photo in the database.
My point is, there are still things out there that have not been done for stock photography. If you look around and use your imagination, you can create something new. Whether these images will be successful or not remains to be seen, but if someone needs it, I have it and there isn't much competition. So get that right brain going and go shoot your unique image!