The Bank of Japan is crossing an important threshold. It's about time.

Once off-limits, an eventual exit from ultra-loose monetary policy is now a public topic for BOJ Gov. Haruhiko Kuroda. In testimony to the Diet last week, he said there are internal discussions on how to begin to withdraw from the bond buying that's kept interest rates around zero. He alluded to the concept of exit last month, also in the Diet.

There are stacks of caveats. It's too soon for Kuroda to reveal the content of the discussions, he stressed. And it's certainly way too soon to start the exit: While Japan's economy is doing pretty well and prices are no longer declining, inflation is far from the BOJ's 2 percent goal. Heading for the doors now would be a mistake.