I think the Wii U will crack 40 million within 3 years. Say two and a half years for 40 million. Jumping the competition by 12 to 18 months, affordable launch price for Wii U and building an insurmountable lead that will not be pulled back.
Next generation may well be a repeat of this generation. PS4 and Next Box both sell over 70 million providing excellent competition but Wii Us lower price more attractive to more buyers will ultimately help it win 8th generation.
Can the PS4 or XBox 360 pull back a 20 million+ sales gap?