I'd wanna see more FR such as Kara-Tur, Thay, Mulhorand, Maztica, Al-Qadim, Zakhara, Malatra, and more.
Dark Sun and Planescape would be epic.
As for MtG Settings, I think Theros or Kamigawa or Tarkir would be really cool, as would more fleshed out and detailed setting guides for Innistrad...