sjarrel, ok it's seems easy to implement. I can make app that will search only for books (in all formats) and will let you to choose app that will open current book. Is it what you want?

walt526, it's possible, but only on rooted firmware (or when SDK will be published). So.., I don't know how much users will want to install rooted firmware, and how much of them will like to pay for an apps which will work only on rooted version. So...
In details.., create an apps will cost me from $500 to $1000 USD, so if there will be several thousand users who will buy it, I can sell it for $1.99, but if there will be only ten people who potentially will buy it, than what price should I set to just cover my investments?