Thank you for the extensive reply! The first part you mentioned is exactly what we were missing back then, we wanted to dynamically generate workflows starting from a configuration selected by the user. This wasn't really possible unless we would generate the YAML openflow specification ourselves.
At the end we gave up and rolled our own simple tool that just does what little we need. This said, it is cool that you are considering offering a more code-friendly way to define workflows. I still think this doesn't offer the same level of dynamism of dragster, where you could easily design branching/conditional workflows. I suppose your considerations regarding the decorators/compilers go exactly in that direction