I don't think it'll happen.
The major reason for increased immigration is purely economic.
Japan has a declining work force and has the most govt debt per
person in the world. (The US has more govt debt outstanding, but a
larger population, so lower per person average)
The only way for Japan to pay back this debt is through
collecting tax revenues hence increasing the size of the economy
and the amount of workers. (Bear in mind Japan's economy has not
grown in 20 years despite zero and negative interest rates at
times)
But just culturally, Japan is a nation that doesn't like
immigration. A lot of Japanese people moved to South America after
world war 2. (The former leader of Peru for example, Alberto
Fujimori was ethnic Japanese origin) Anyway, descendants of these
Japanese immigrants were offered jobs in Japan as guest
workers...mostly working in factories and other "blue collar jobs"
lets say. In 2009...the Japanese paid these people money to go home
and give up the right to work in Japan again.
An old article can be found here:
http://www.nytimes.com/2009/04/23/business/global/23immigrant.html?pagewanted=all&_r=0
So I think if the Japanese cannot even open up their country to
people who are Japanese descendants...and can establish direct
links to the country...I can't culturally see them being accepting
of large scale foreign immigration.
Who knows they might get more desparate in the future...but
these kind of attitudes are ingrained and I think take generations
to change. And by that time it might be too late.
There are several big Hedge Funds worldwide who are convinced
this will be the case...and are betting that the Japanese govt will
default on it's govt debt....which would be a major economic shock
worlwide.