I just feel like, as probably a bigger reader than most, I could only identify a handful of pre-1800s books by first passages (call me ishmael?). I thought this was an interesting concept but ultimately I don't see a way to become popular / viable.
Now that said, and also just a thought: The idea of motifs recently came to me for a similar book project (for example stephen king and alice munro are linked by the "small town secrets" motif). that's something more relatable that you might be able to gamify. Thoughts?