I think it would be a bad idea to put major attractions based on Disney movies and characters in World Showcase pavilions. I think it would be a great idea to put major attractions based on the countries and cultures themselves in World Showcase pavilions.
I love Grand Fiesta Tour dearly. I never saw Rio del Tiempo. Though it could be improved in this area, the Tour is more focused on the sights in Mexico, with a loose storyline featuring the characters.
An Alice in Wonderland ride would have nothing to do with the United Kingdom, besides the fact that the story was written by an Englishman. It would be like putting a Wizard of Oz attraction in the America pavilion.
Though I haven't experience Maelstrom myself, I've seen many a video of it and enjoy the concept very much. EPCOT Central did a good blog post about why Maelstrom is one of the best attractions in Walt Disney World.
The problem is, originally, most of the WS attractions originally planned were boat rides. Mexico, Norway, Germany, Italy... The themes of these attractions really limited the ride systems.
Everyone loves the opening sequence of Peter Pan's Flight, right? What if there was a small-scale suspended dark ride where you fly over sights of the United Kingdom at night? A little more realistic than Peter Pan.