That's awesome. I didn't know they had actually finished it. Finally, a ride dedicated to my favorite disney animated movie. I can't wait until 2009 so I can ride this thing like 5 times.
If any new countries DO get added (seeing that it's been about 20 years since a new country's been added, it seems less and less likely) I dont think they will add any more countries from places like Africa, South America or even Asia for that matter. In case you havent noticed there are places in Animal Kingdom that carry African and South Asian themes much like they were countries in world showcase. I think that if they add animal pavilions from South America and even Australia, they would do the same thing.
Any new countries that are added to World Showcase would probably be "western world" places like North America/Europe/Middle East countries.
My top two suggestions are Greece and Russia. They are pretty easy to make by my opinion. I wouldnt count on any Middle Eastern countries (not even Israel) making the cut less you wanna cuz controversy!