Seems like it would be the next logical step to your solution. Giving developers a type of API where they can create hooks into your application. Then at the user level we can configure what service / function we want to associate when that selected icon is selected. That being said might be a good idea to add in a few "extra" icons for future development features so you're not limited to what you have now (more is actually better in this case so the books can scale as you expand your solution).
Would be very useful for helping this whole project last long term, lots of new unique ideas could be tested
You can assign the icons yourself when you first set up the book and app together. I think the customization is a good idea but has to come with additional updates and connections to other software and application in the Rocketbook scanner and app.
Maybe we could specify one service as a URL where a POST request would be made with a specific page. Some metadata using HTTP Headers and the page as the request body. This way would be simple for developers to create their own servers to receive the files.