We are at the point where build automation wants to use daffodil, not just our own automation, but that of third parties, or associated with the authoring, compiling and testing of a DFDL schema separately from daffodil itself.
So we need a way to package daffodil such that it can be integrated into build tools that don't just run CLI-style commands. I.e., for sbt, that's an sbt plug in. Probably something similar for maven.
Note: Basic build tools like make can just use the daffodil CLI commands.
I'd say these plug-ins should be part of one of the daffodil jars so that getting the distribution gets you CLI, jars for API-level use, and sbt/maven plug-ins too.