I believe this 3 column design with a largely empty and unused first column is a massive waste of space, especially on technical sites that often use wide code segments that then needs to be sidescrolled to be fully read. Everything that's in there should be where it is now or in a burger menu (this appears to only happen on very narrow displays on SO).
But I am certain this has been mentioned and ignored before...
Other than that: Will the new layout have better support for the small mod box on the left side that disappears on narrow displays? If not: Why?