I think Philip VanDusen is right on the mark and pretty much all of these trends can be used for book cover design.
Since starting my own business, I have created more than 2000 book covers for large, traditional publishing organizations; small presses and indie publishers. My clients have been featured in numerous high-profile media sources including Oprah, 48-Hours, People Magazine and the Today show. I'm closely supervised by a small herd of rescue animals including two very large dogs, a cat that I'm not sure likes me very much, and a three-pound bunny who runs the whole show. When I'm not designing book covers I'm usually working on newsletters, infographics, signage and posters, or writing articles.