It's much further along than I would've anticipated. I'm not sure if it was under development by someone during the design phase or not, but it appears it may have been.
Development is going to take place on Github this go around, which is different from past default themes and should significantly lower the barrier for contributions. If you're a themer and want to get involved in WordPress core development, get on it. Meetings for the theme development will be on Fridays.