Japan should defenitly start accepting new immigrants (from non-asian countries as well), not even because of the rapidly aging and shrinking population but as an effort to move into the 21st century. Japans unwillingness to accept foreigners is not only going to hurt it's economy in the future but is also going to make it ever more alienated from the rest of the modern world that has accepted and, in many more ways than not, made immigration work. Not only that, but it will bring new ideas, creativity and perspectives to the country rather than letting it become a static society that slowly stagnates under it's own unwillingness to change.
It's been stated again and again and again that "Japan is not like the US, they're not a melting pot ect". Japan is one of least culturally diverse first world nation so there's almost no chance of that happening, but it seems like Japan is doing everything in it's power to head the issue off at the pass when, so far, the possibility isn't even there. They are jumping to conclussion about what might happen if they allowed more immigrants, fearing turning into another US or Canada.
I know there is a resistance of change and conflict but, honestly, is Japan such a delicate flower that they would crumble and die at the first major conflict? Methinks not. The only problem really lies with the Japanese people themselves. I don't know what they've seen of the US or Canada that makes them so scared of turning into a multi-cultural society (maybe someone living in Japan could tell me) but I'm sure that wont be the case.