Have you ever given any thought to offline content for the forums? Some of the most useful tweaks I've made for Opus are nuggets I gleaned from reading forum content, and clicking, pausing, reading is rather cumbersome. Someone has started working on such as reader for Discourse. https://github.com/etewiah/offcourse
The F1 help manual works offline.
Not sure an offline copy of the forum makes much sense. A full copy of the forum is approaching 3GB, compressed, which not many people would want to download and keep up to date. What would the benefit be? Are you somewhere without always-on internet? (I'm in the middle of nowhere and still have that. :))
For me it would just be a faster way to find items of interest--I spend my time fixing other people's computer issues and rarely have time to spend on mine. I tend to explore the forums and experiment with features for a day or two and then get back to work for days, week, sometimes months. Browsing the RSS feeds with Feedly was faster, but the large fonts and white space used by Discourse, while attractive, make browsing and speed-reading cumbersome. Unless I'm missing the way to add RSS feeds for the forums (Opus News still functions.)
Try a ".rss" at the end of URLs.
Oops! Thanks, andersonnnunes.
But thanks Leo for being able to edit this.
Wasn't me. 
We're all Leo 
All members are Leo but some members are more Leo than others.
--Leo Orwell