There’s a Community Wiki for Custom CSS Snippets and there’s the Show off Your Dashboards thread for sharing cool designs. We could certainly create a category for sharing themes if there’s enough interest.
We had a variety of discussions around sharing themes during the development of the feature. I think the first step would be to get a proper Theme Export/Import feature in place so it’s easy to share cool Themes like this.
Then the next step would be for people to share their themes! If there’s enough interest and the theme author is willing to have their theme included, I would be open to including popular community themes.
Edit: @Justin1 I moved our posts into a new thread with a more relevant title so hopefully other people can see it and join in on the discussion!