Will Japanese music ever achieve mainstream success in America?
Music, no matter where it's from, is strongly rooted in culture. Unless the popular culture that the Asian music is rooted in somehow survives the trip to American shores, the experience of said music collapses like a house without a foundation.
That said, there's just too big of a gap between Japanese culture and American culture.
What is Japanese culture's attitude towards the following?
2) How a male should act/dress/talk
3) How a female should act/dress/talk
Now what about American culture's attitude towards those same topics?
The difference is really quite obvious.
Just look at how differently the two cultures handle romance. An exchange of words that would be considered "sweet" or "honest' in Japan would be laughed upon as being "corny" in America.
A lot of this cultural difference rubs off on the music. Hence the barrier.
The music from Taiwan and Korea are in the same situation. The way that romance is handled in popular culture is very similar between Japan, Taiwan, and Korea (and I suspect other regions in Asia as well) -- they share a similar "contemporary cultural language," so to speak, and so that's why it's easy for popular culture to mix in this region.
There's too big of a cultural difference across the Pacific, however. I'd put my money on "no" as the answer to the question.
Will a Japanese artist ever achieve mainstream success in America?
In the foreseeable future, short answer: no.
Not unless that artist is willing to give up everything Japanese about his/her music in the first place.
Which begs the question: why even bother, then?
Not that I'm complaining about Japanese music not becoming mainstream here, however. The Japanese artists would need to sacrifice too much for the sake of becoming "big" in the US -- it's really more of a cultural barrier than a language barrier.
My experience with American music is an example of the culture barrier. Spending my early years in Taiwan, I had plenty of exposure to (obviously) Chinese music and culture. Japanese popular culture was (and still is) really big in Taiwan, so I got plenty of that too.
Moving to America gave me access to American music. I started listening to Korean music last, but I was much fonder of it than I was of American music was, due to the similarity of the "contemporary cultural language" that I talked about above.
American music still doesn't click very well with me. Of course there'll be a few songs that I happen to find that I like, but even that hasn't happened in a very long while. Language can be translated, but are we supposed to do with culture?
My friends can poke fun at my "Asian music" all day long, but it doesn't change the fact that I think the American music they have in their playlists sucks.