I think it's a noble effort to popularize org-mode and to make it easier to use. And I learned today about mixed-pitch :)
However, a lot of visual configuration depends on fonts, colors, and other things which may vary a lot between users. While most of us by now probably use a graphical version of Emacs, any such default settings should be done with care for users who still use Emacs on a pure-text interface.
Making some default prettification as part of Spacemacs's org-mode layer would be nice, since it includes a lot of customization and eye candy already.
All the best,