I don't see the idea of going all out mainstream a particulary good one. Why?
Say if you started developing this 3rd person shooter of yours filled with obvious steals. Say you would decide to start doing the initial research today and excpect release in late 2012. Then, in 2012 you would sit there with your "2 and a quarter-life" who would have been a smash hit in Japan in 2009, and someone else, maybe gamesas, came up with this crazy idea of developing something radically new, never seen before game concept back in 2008. And their innovative attempt would be praised for bringing some much needed change into the gaming world. And also, if you go mainstream, the chances are your game would be just "another brick in the wall" to quote Pink Floyd. It's the pioneers of their genres who stick out, those who dared and won instead of going the "safe" way.
Gaming trends are just like any other trends, they change, and sometimes quite rapidly, why? Because someone has come up with the next big "thing". When you sit down today to start development of a game, you'd have to come up with a concept that would sell when it's released, you can't base it on the present facts. No, you have to be a visionary or psycic of some sort to see what the future of games will look like and what will sell. This is where the tricky part of doing business comes up. Gambling. You dream up this great vision of a game to be released in a pretty uncertain future, generally speaking.
As far from originality = no sales, I beg to differ. Let me just pull out one prime example of quite the opposite. Just recent years one specific game, it's sequel and numerous expansions tried something like nothing seen since it's text-based predecessors 20 or so years ago. This series has sold incredible amounts of copies and anyone who's gotten past free-cell in computer gaming, are extremely likely to have tried this game. What game could this be? First one to figure it out gets a complimentary Vault-Tec approved thumbs up from me.
So what you need to do is, ask yourself one question:
"What kind of games do I/the world want to play in the future?" Renesco the rocketman