I would be absolutely appalled if Disney installed roller coasters and other amusement park rides in World Showcase. That would utterly ruin Epcot.
World Showcase should be about the architecture, foods, beverages, traditional culture, popular culture, history, and how people in those countries have fun. World Showcase should be be fun, enlightening, and delicious. It should immerse you in other lands.
World Showcase should not be an excuse to have the Mexican Revolution Looping Coaster or the MorocCoaster. Fortunately, I don't think there are any executives in the Disney Parks & Resorts business segment who would do something that stupid.