I do wonder if they will actually have any chance at mainstream success. For years, the only Japanese acts that have had any kind of semi-mainstream relevancy in the West is metal acts like Coldrain, Crossfaith etc - and that's existing within the very specific metal niche, where there's much less bias about where an act is from.
I think it's great that more JP acts are actively looking to the West now - but I think I'll believe it when I see it in terms of say, I dunno, an act like One OK Rock getting a legit Top 40 hit in the US or UK. But they do seem to be making all the right moves though.
I think looking at the recent success of acts like Twenty One Pilots - it shows there's certainly scope for acts from outside the obvious pop sphere to break through to legit success with the right ingredients in place.