The problem is sony doesnt have 2 years. Only the snes made a comeback from a late launch, no other console managed that. If sony keeps trailing the Wii in Japan as they do now than by the end of the year the wii will become the main platform for Japan. Sony still has some of its big guns for late 2007, beginning 2008 if everything works out so that could make the impact sony needs but if you look at what software japan bought for over the last 12 months that might not be what sony needs.
I wonder why people always think like this? Wii will never be the main platform for any third party developer, excluding the mini-game making companies. Most of their games cannot be made for the Wii due to its lack of power. It's a technological limitation, not economic. So even if the Wii sells 20 million, most of the traditional games will still be made for the PS3 and possibly the 360.