Doesn't seem like that bad of an idea to me. After all, it's a pretty well known fact that languages are often easier to learn when a student is younger. I started studying French in school when I was around 6 or 7, and while I wouldn't say I'm fluent, I can speak it fairly well and carry on a half-decent conversation. Now, I'm seeing students who are in their mid-teens who are studying french, and some of them can't even count to 50, or ask for permission to go to the bathroom, or even say their own name in French.
I'd say the Japanese introducing thier kids to English early on is a good thing, but not necessarily preschool. Make it elementary school instead. If they wait until the kids are in 12, as the article says, by that time the kids' just won't have the ability to absorb it all as easily as they would have if they had started younger.