I really like the suggestion 🙂
In PC, I think we could simply replace/hide the site name and links with the discussion title when we go to a discussion.
And the tags, put them just below the title. Also, we could put the logo to the left of the title. Our favicon, more precisely.
I hope I've made myself clear.
For mobile, I don't see any solution other than adding a little line that just puts the title. Without the tags, otherwise it would be too big.