Epcot is my favorite park & I would love to see countries added. I also love Puerto Rico and think it is beautiful. I do NOT, however want them to have a pavilion in world showcase. They are part of the United States. They are a commonwealth, which is higher than just a territory. I do think they will become our 51st state at some point.... but even as it stands they are US citizens and I don't think having two US pavilions is good. Hawaii has a very different native culture from mainland US but we are not adding a Hawaiian pavilion. It's just my personal opinion but I just think it would add to ignorance. So many people don't even understand that Puerto Rico is a commonwealth.
I'd love to see new countries that would showcase more of the world though. Brazil, Peru (machine pichu), Argentina, New Zealand, Australia (the outback), United Arab Emirates (now they could afford it), Egypt (pyramids), Zimbabwe (victoria falls), Russia (Kremlin), Ireland (castles) .....just to name a few that could be cool to see!