As @Foxaii suggested on GitHub I created a non-destructive fork of roots that disables all public facing comment code. Regardless of the Wordpress settings nothing concerning comments will be rendered on public facing pages/articles/* – no forms, no content, not even the annoying “Comments are closed” message.
Extending the custom function in lib/custom.php would make comments possible on selected items possible, e.g. by using is_page().
Should be useful in case selectively allowing comments are a desired feature and until Wordpress offers a similar option itself.