Poor person's recipe for a "federated" experience of large numbers of #discourse forums:
1) start with your favorite #rss client (I currently use #akregator)
2) create a folder named "Forums"
3) visit the forums you want to follow and copy the URL
4) click the "add feed" button of your client and *append* URL/posts.rss (discourse will not serve the rss url by default)
5) Done. When the #fediverse catches up you will be able to upgrade your #opml into some #activitypub thingy