Isabel Reynolds writes for Reuters:
"With more than a quarter of Japanese expected to be aged over 65 by 2015, the country faces serious economic consequences, including labour shortages that could weigh on GDP.'
"A group of ruling party politicians see immigration as a possible solution and have presented Prime Minister Yasuo Fukuda with a radical new proposal that seeks to have immigrants make up 10 per cent of the population in 50 years' time. Government figures show the workforce is on course to shrink by eight million in the next 10 years."[Japan gets serious about immigration, August 09, 2008]
Now, of course, what could be considered instead are immediate economic incentives that would make it easier for young Japanese to have families. Sweden has done that-and has a higher birth rate than Italy—which hasn't followed that path.
That won't solve the immediate problem—but it would create the possibility of a longer term stabilization.