Shortcodes are a real problem if you want to publish the full post content. Take a look at the Dealing with WordPress shortcodes section of this topic for a few ways of dealing with them: WP Discourse Plugin Tips and Tricks.
The easiest approach would be to publish an excerpt of the post to Discourse and then allow users to see the full post by clicking on the Show Full Post button. When that is done, the shortcodes should be properly rendered in the expanded post.