What's the chance it will actually see the light of day?

I'm going to speculate.

20%

Thats realistic. All the good book series have the chance, but never make it to the screen. The problem is that no one wants 30 million books on screens all long and never-ending. If we wish to them produced they'll have to be nonexistent.

The reason is because most adaptations fail. It's very hard to adapt a good book without getting a hard time by fans and it's very hard to adapt a terrible book and make a decent series or film. Also if the book's premise, story and plot isn't that good then you might as well write something new.