I posit that Japan is able to keep its "exoticness" (to much of the world) as a culture because the cultural osmosis that comes from having a populace with good English skills promotes homogenization. I imagine a Japan that's highly fluent in English will look a lot more similar to S. Korea.

I might go to extend this theory and say the quality of English literacy in Japan is intentionally kneecapped at some level in an attempt to retain their cultural identity, even if unconsciously.