Ideas are cheap. Don't hoard them! The proof is in the execution.
Start writing the book. Here's what might happen: you might create a masterpiece. Or you might discover that the idea doesn't really work at all. You might spend months typing away and discover you want to throw it all out. You might fall into a pit of despair.
And then one day you'll wake up and realize that you've got ten new ideas. And then you can start turning that into your masterpiece.
But if you really want to do this, start sooner than later. Because ideas are cheaper than years.