If I were to guess, I'd predict the PS4 sales to be right in between the PS3 and PS2 sales, so that means about 115-120 million units. I don't think it will dominate like the PS2 did, but the market is growing, and it should start out incredibly strong and continue on with that momentum due to a strong library of games.
I don't believe in the value of Kinect 2.0 and the 500 dollar price tag, I think the XB1 will struggle everywhere that isn't North America. The Wii U should rebound as it's the cheapest console that has a strong 2014 library of games, and casuals will flock to it when it's 200-250 dollars like the Wii was. I'm going to assume next gen will be as long as this gen (so 7 or 8 years)
Listing them out:
PS4: 115-120 million units
Wii U: 80 million units (I doubt many have Nintendo nearly this high)
XB1: 45 million units
3DS: 160 million units
PS Vita: 25 million units (last Sony handheld)
Human contact, the final frontier.
