I don't think that it would be that hard to explain the plot in a movie version. Basically they would just make the adventure shorter. Basically it would just goIt would be possible, but it would take a long time to explain the plot, like other worlds and many things may be left out to make the flim a fair length. And characters may be changed or new ones added to Americanize the movie for the general public. Dragonball Evolution ring any bells?
-Destiny Islands
-Traverse Town (explain heartless and keyholes)
-Agrabah (explain princesses and show a keyhole)
-Monstro (show riku's turn)
-Hollow Bastion
-End of the World
And if anything, they wouldn't even have to show the entirety of Agrabah, just showing riku's sillouhette carrying away Jasmine. Maybe they can put in Neverland, but, they wouldn't even have to show that much of the game. Just the major points. And a Chain of Memories movie would be as easy as f***.