We do have the beginnings of a scripting API already built into Dorico, using the Lua scripting language. At the moment, script plug-ins are limited to the sorts of things you can do in a macro recorder, i.e. triggering commands that are in the user interface. This can be useful for batch processing operations, but as yet it doesn’t really provide much access to the internals of the application or the music you write.
Over time we hope to broaden and deepen the API so that the kinds of extraordinary plug-ins written for Sibelius by legends like Bob Zawalich and for Finale by people like Jari Williamson can be written for Dorico as well, but like many other aspects of our development, it will take a little while for the application’s capabilities to match up with our aspirations!