TextFlow is a open source software and we encourage users and other developers to contribute with the project.
The main place to follow the TextFlow development is the Launchpad Project site. There you can report bugs, ask questions, propose new features and browse the source code.
If you want a more simple way to see the development you can access the TextFlow roadmap. It shows the features that will be in the next version and their status (implemented, in progress or not started).