Call me when there's an option for Planescape.
It's an interesting omission: almost strange considering Chris Perkins' design background with Planescape. He's even tweeted that it would be his first pick for a setting to bring back in 5th!
https://twitter.com/ChrisPerkinsDnD/status/623187432431751168
Speculation? Planescape is already in the works. That's why Perkins didn't add it to the poll.