As PKMNBlogger said, Pokemon's run out of Japanese prefectures. So, everyone thought they would start being based off of American states, & turns out, we were right. &, yeah, I agree with the 2nd thing.
We haven't run out of Japanese prefectures
yet:
*pulls out Pokemon region composite map again* :\
There's a
large swath of land available to the north of Kanto and Johto, as well as a smaller sidequest-sized chunk to the left of Johto. The usage of New York City, IIRC, is
partially due to Junichi Masuda's engaging experience there, viewing all of the diversity presented before him as he toured there. AFAIK, neither Japan nor the United States have been ruled out as potential inspirations.
Anyway, more on-topic, seeing Lt. Surge's house in Unova would *kind of* make sense, due to Unova=part of America. Or, Game Freak could save his house for another U.S.-themed region. I kind of wish we could have avoided this "real-world references in games" thing, because
technically Unova is
entirely different from the United States of America. This is kind of similar to that thread discussing whether Mewtwo could be featured as well, due to him being seen cloaked, standing in a New York City-ish city in the movie
Mewtwo Returns.
It would be cool if Lt. Surge and Mewtwo visited Unova to make cameos in
Pokemon Gray Version, though, due to their (partial) affiliations with United States-related areas as depicted in various
Pokemon media.