To address some of the ideas expressed here...
I would NOT want a Lion King attraction set within MK's Fantasyland, which seems to be quite a popular idea. I don't think the setting would be at all appropriate. The Lion King occurs on a grand scale with lush backgrounds. It clashes with the Medeival Faire Fantasyland that we currently have, with storybooks and classic British literature dominating. I think AK is a much better candidate for a Lion King attraction, after relocating FOTLK to Africa and building up this section of the park.
I like the idea of a Little Mermaid attraction, especially near the Grotto. I think that if it is a moderately themed building, the attraction would be perfect.
Mary Poppins also seems like a suitable candidate for a ride. It's a classic story, and a dark ride woudl be wonderful.
Aladdin, I would prefer something big (and different) somewhere else. I just don't think Aladdin belongs in Fantasyland or Adventureland. Maybe something in MGM, since that's just a mixmatching of movies anyway?
Mr. Toad is gone. Fantasyland rides should be based on recognizable classics, not obscure animation choices.
NO to the Matterhorn. If you want to ride the Matterhorn, go to Disneyland. or Animal Kingdom.
I don't even know about the addition of dark rides. Sure, the 20K spot opens up a ton of land, but I don't know if I want to see more plain dark rides in Fantasyland. They already dominate the area. Possibly an immersive attraction, similar to Splash Mountain, that combines dark ride elements in a physically pleasing setting. I like the idea of a Bald Mountain or Villain Mountain. Fantasyland should be family friendly, so it shouldn't be tooooo scary, but I think it's already viewed as the home of little kids. A thrilling adventure would be perfect for the area. To see the Disney Villains come to life would really spark up Fantasyland's attendance.