I'm currently trying to remember the name of a book I saw in a book store so I can buy it on Kindle, so, in some ways, I'd say you would have a user today.

HOWEVER, what are you really offering here? Do you REALLY think you can do a better job of search than google or amazon? That is absolutely what you are up against.

I think the idea of contacting publishers to ask their opinion is useless. They'd say 'yes', if it meant more sales, this is a dying industry, they want anything that 'might' help them.

Keyword search is likely not a good idea. How well do people remember the color of a book, or how good are they going to be at describing what was on the cover.

You've got a potential market, but I think you're going about it the wrong way.

What about an app that lets a user take a photo of a book, and then you match that to where they can find the book online?