In World Showcase, there’s an expansion pad between practically every existing country. The only ones that are compromised are the ones where they put the Frozen meet and greet between Mexico and Norway and the one that’s half taken over by Ratatouille between France and Morocco. Realistically, I don’t think they’d ultimately use them all for countries or else it would become super dense. If they wanted to continue to space things evenly, they could easily fit two more (one at World Showplace, one in front of the former barge storage area). After that, they should be judicious about whether they use the pads for countries or attractions, in my opinion.