Worst case predictions:
Xbox 360: 25m - X360 starts tracking more like the Xbox in US/Eur, and ends up slightly ahead in Japan.
PS3: 20m - Tracks similar to what it is now, and no real major defining bump once all games come out. Ends up at GC-esque levels despite FFXIII, MGS, GT, ect. Sony bails in 2009 for a cheaper console and pulls the PS3 plug (skynet fights back), while PSP sales still drive some remote profit.
Wii: 25m - Christmas 2007 ends up being a deathblow to Nintendo, as HDTV penetration is through the roof, MS and Sony drop major price bombs and consumers in the US and Europe start trending more like last gen, leaving the Wii at GC-like levels. Japan remains OK, but still trends better than USA and Europe. Nintendo pulls the plug, and releases Wii 2 in 2009 with a much superior hardware system, and tries to renew a fight vs. MS and Sony.