great idea! i wish you much success! i am in a similar place of identifying what do i really want to do -- and entrepreneurism is where i'm landing as well, although i want to do for plus-sized clothing what you want to do for fast food -- make it good!
anyway, there is a place in brooklyn called "foodswings" that seems to get a lot of business. they play up the "vegan fast food" aspect -- it's not healthy, it's decadent and vegan.
i dont think it's exactly what you're going for, but i thought you might want to check out their menu and such:
Foodswings - NYC Restaurant & Menu Guide. Menus, Ratings, Reviews. New York City, NY