I predict around 50-55 million when the PS3 has stopped selling. Has a small chance at 60 million if things turn around, but higher than 60 is near impossible.
To put it in perspective:
360: 60-65 million
Wii: 140-160 million
PS3 and 360 selling even close to 60 million will probably mean Wii has breached 200 million easy, that's the only way the market will be big enough
Predictions:Sales of Wii Fit will surpass the combined sales of the Grand Theft Auto franchiseLifetime sales of Wii will surpass the combined sales of the entire Playstation family of consoles by 12/31/2015 Wii hardware sales will surpass the total hardware sales of the PS2 by 12/31/2010 Wii will have 50% marketshare or more by the end of 2008 (I was wrong!! It was a little over 48% only)Wii will surpass 45 Million in lifetime sales by the end of 2008 (I was wrong!! Nintendo Financials showed it fell slightly short of 45 million shipped by end of 2008)Wii will surpass 80 Million in lifetime sales by the end of 2009 (I was wrong!! Wii didn't even get to 70 Million)