According to this GI piece, former SCEE chap Chris Deering’s said that he believes Nintendo and Sony will tie in this generation’s hardware race by 2011. From the story:
The EIF chairman presented figures he arrived at by triangulating Screen Digest and IDG data. He also took into account factors such as the growth of hi-def and the grey gamer market, the emergence of new game engines and increasing ubiquity of wi-fi access. He said the active installed base for hardware is set to rise from 316 million to 500 million over the next three years, with “two big mega-powers” leading the charge.
According to Deering sales of the DS and any future iterations of the hardware will reach 150 million by 2011, while the figure for Wii will be 80 million. He predicted the installed base for PS3 will be 70 million, and said for PS2 it will be 90 million and PSP will be 70 million. In other words, Sony and Nintendo will each have sold 230 million machines.
More through the link.