There's a severe lack of modern-themed RPGs. Well there's Alpha Protocol, The Secret World, and...that's about it. I think a modern themed RPG has a lot of untapped potential. For one, most "modern RPGs" that were released usually cross over to the science fiction part. I don't think I've yet seen a pure modern RPG, so as an idea, that might be a starting point.
I'd also recommend a setting in Hyboria aka Conan's universe, but then that's the Conan fanboy in me speaking already hehe. Not so much recommending it here, since it's not wholly public domain, but just to elaborate on a unique point about it, the cool thing about Conan's universe is that everything envisioned about it is based on real history. Although Hyboria is fiction itself, the setting is built as an emulated layer to real world history that took place during the BC eras. This creates a sense of connection with the reader, something that we can empathize with. Maybe we can try a theme eg. modern world that does this too.