The plugin now has Visibility support. You can now make Notes, aka Mastodon statuses, public.
https://github.com/discourse/discourse-activity-pub/pull/19
Next up is adding Article support (for long-form content) and improving the content parsing.
https://github.com/discourse/discourse-activity-pub/pull/21
After that will be Full Topic support, which is almost ready. Here’s a little preview
(and yes, it is compatible with FEP-1b12)