Leaning more towards a book on the mental game. Most of my graduate hours are in educational psychology.
The main goal is not to beat the proverbial dead horse. I want to write on a subject that has very little or no writing on it.
There's definitely room for more material on the mental game. The few books available that are relevant to pool hardly exhaust the subject.
My favorite is
Pleasures of Small Motions by Bob Fancher. Fancher can write well, he has solid credentials, and his material agrees with what I've read in other books about how the brain actually works. For me it's just the right mix of the scholarly and the down-to-earth.
http://mind-for-hire.com/
The Inner Game of Tennis by Gallwey is a favorite for some shooters. I just purchased the book, and in the half I've read so far the author presents ideas simply and effectively. His advice doesn't contradict what one would find in Fancher. That said, the references to (pseudo-)Zen and pop psych mark this book as a product of the 1970's. It reads like one of the better business management books: catchy and simple, but a bit too caught up in cute metaphors. Not surprisingly the author has spun the book's success into a business.
http://www.theinnergame.com/html/about_tim.html
A Mind for Pool should be mentioned, too, though of the books I've read by Capelle it's his weakest effort. His usual method of cramming a lot of information in a honkin' big book doesn't serve this subject well: a book on the mental game should remain focused and sharp. The poor editing as well as Capelle's weakness for bullet points and graphical clutter further blunt his message. Though Capelle can't write with the same authority as Fancher, he does have good points and it's a shame they get buried.
Lastly, just today I watched a video series by Blackjack entitled "Mental Training Techniques":
http://www.youtube.com/watch?v=CQrGTbkvj4M&NR=1
I like Blackjack's focus on practical exercises, and in his written material I've appreciated how he presents the thought process of someone reading a rack. He's effective at putting the reader "in" a specific situation, which I believe helps immensely.
If your background in educational psych equips you to write a focused book rooted in well-established principles, and if this book provides simple, practical methods for improving one's mental game, then I think you'd have a winner and I'd line up for a copy.