One skater I can think of from ages ago who did very well skating for another country was Dianne de Leeuw. She was born and grew up in the U.S., but her mother is Dutch and her father has dual citizenship, so she skated for the Netherlands. In 1975, I believe, she was World Champion, and she was a strong contender for the 1976 OGM. She won silver behind Dorothy Hamill. Skating for the Netherlands, she was able to take part in the European Championships, and one year she won that. According to Wiki, she now coaches in California. Clearly it was smart of Dianne to skate for something other than the U.S. at that time, in such a crowded field, and she had the opportunity of representing a country in which the last major skater was I think Sjoukje Dijkstra, who won the Olympics in 1964. In other words, the Netherlands was just enough of a skating power to give a boost to a good skater, but not enough of a power to have a crowded field.
And then of course there's Misha Ge. I had to look him up because he's a walking, talking United Nations: part Russian, part Chinese, part Korean, lived all over the place including the U.S. This is a guy who should consider skating for Korea, not Russia