Spain would be a GREAT addition to World Showcase IMO. Best food in the world, and beautiful architecture and artwork as well. In other words, they have PLENTY of culture to share. As someone fluent in Spanish and who has spent a bit of time of Spain, I've always been a little put out that Spain is the only Western European country that got the shaft from World Showcase.
I'm thinking maybe some Gaudi-esque architecture, perhaps a small replication of the famous bench from Park Guell. Then have some grand Castillian architecture like what you'd find in Madrid, and some of the intimate Gothic alley ways and bridges like what you'd find in Seville. Throw in some sculptures by Picasso, Francisco Barón, and Joan Miró and you're golden.
Not to mention that a Spanish pavilion could be the Churro Central for WDW. :animwink:
I've been a major advocate for a Brazil pavilion as well, I've thought that since Brazil is a nation most particularly famous for its natural beauty, perhaps a "natural" icon might be more appropriate. I'm thinking perhaps a replica of Sugarloaf Mountain from Rio de Janeiro. It could even hold a showbuilding for a ride inside - a skyway-type dark ride, perhaps?
Then you could have a charming Brazilian seaside village at its base, or a jungle walkthrough representing the Amazon rainforest, with waterfalls, lush jungle landscaping, and sounds of wildlife.