Hi grimlock,
with articy:draft 2 you can only the API to write a stand-alone program that works with articy:draft data. This requires the API license with a additional cost.
The "Macro devkit" for articy:draft 3 is free of charge and allows you to write plugins that integrate into a running user session.
It was called "MDK" because it does not allow to change the appearance of articy:draft or add buttons to the UI, you can "only" add commands into the context menu or a global entry of the ribbon bar.
You also can hook some callbacks or events where you can react on user actions or can disallow some actions if you like.
But to come back to your main desire you sure can add a globally available entry to start a custom written XML export. The MDK API gives you methods to start long running tasks like an export with progress bar and message window like other tasks of articy:draft also do.
You might take a look at our released plugins, they are available on our download page (
http://www.nevigo.com/en/downloads/#plugins ). We provide the installer and source for each of them.