Drupal initiative work is spinning up. Research, planning and scoping things. Important, but up till a point. Many of the changes we want to bring to core for Drupal 8 can be done as contributed projects right now.
Starting in contrib has some important advantages. You get to ship your project earlier and more often. Drupal 7 sites can benefit from your solution. The code and concept can be tested and improved based on feedback coming from actual use in the wild.