That's what people here don't understand.
Unless both Japan and NA massively ask for it, it won't happen. As for EU, it doesn't matter, because EU players can easily play with NA people on a NA hosted World, latency wouldn't as bad as with a server located in Japan, there wouldn't be any language barrier either (most of EU players speaks EN).
So NA players wanting to play with everyone is one thing but does JP players wants to play with them?