I would say, that the todo list should look like this:
- Create a (small) photo book in Scribus manually, to check if it is the right tool.
- I can write a Lua script, that exports the selected images in darktable and starts scribus with parameters. (It is possible to start Scribus with parameter, that runs a script in Scribus.)
- We need a Python script in Scribus that does the work there. There are already the scripts @paperdigits found. Someone needs to modify this scripts to run with parameters from the command line and without GUI.If that is done we can call this script from the Lua script in dt.
The ordering in darktable is a minor point and could be earliest fixed in a release next year, because dt is in feature freeze for 2.4. Perhaps you can write a bug report with a detailed description, how this should look like. It is possible to tag photos in dt. And it is possible to write a simple Lua script to export the selected photos and name the files like the tags. But that is of cause not very user friendly.