I've read the redesign threads over the past few years and participated in many of them.

One argument that's common but a fallacy in my opinion is that the site should have less color. The maquette you're showing takes away many of the colored elements and seems to tend towards chromatic minimalism but, let me stress this: you're taking away eye candy that's made the dark theme very appealing! If the SO dark/light theme becomes more bland less users will enjoy it, imo, less.

I think a key historical post that defines the limit of color use in the theme is New post summary designs on site home pages and greatest hits now; everywhere else eventually by Ben Kelly and the design team back then - to this day I am a fan of their work. I am convinced -having followed events carefully at that time- that the post's score and the reactions were to a significant degree overdetermined by the historical context that might not be apparent in hindsight if you weren't around as events unfolded (with many of the said events, being site changes that weren't design related).

The particular historical context (as I see it) was of a major site redesign that saw many launches over months that were riddled with bugs, for example the 241 answers under New responsive Activity page was just one of them. So at one point the community became saturated with the constant changes and I saw several users who are consistently soft-spoken criticizing the design team harshly over minutiae. (You have to appreciate, as an SE designer, that if you try the userbase's patience often enough in a short amount of time, eventually you will trigger users on a bad day where design criticism becomes the motif of their personal catharsis that day, and the worst that can happen is a crowd frenzy of reputation fueled criticism.)

So, in short, in this case: less color really is less. And that's the problem: it just feels like... less.