Stage Three (the rooftop) became available in today's update.
Be warned - Zoot and Beaker are both in the lineup again, and those were the two hardest for me to digitize in The Kitchen. I expect their likelihood of success will be at LEAST as low as before, if not worse!
And for people who can't wait to hear the entire song, there's apparently a "full stage" of The Rooftop at #6 in the weekly Top Stages rankings. (Which definitely makes me question the credibility or accuracy of those ratings - as well as wondering if someone was actually crazy enough to spend the thousands of diamonds it would take to "speed unlock" everything that fast ...)