I think New Zealand would be an excellent addition, mostly because it's not as high profile a country as the ones mentioned above and because it's such a versatile country, so many different things, that I think it would just be so interesting to see what would be incorporated in a WS pavilion.
I'd like to see a regional US section opened up. They could have a surfing type ride to represent the west coast, cajun stuff for Louisiana, southern comfort foods for the south, they could show how snow is made to represent the north, etc. I know there are several visitors to WDW that have never seen snow and would love to see snow. I'd also would love for them to have something to represent each of the states. Like a little museum or something.