Nintendo has never done anything quite like this with one of their franchises, it's an experiment of sorts. I see people trying to use statistics of previously released games to set some sort of a bar or measuring stick but it's not going to work like that. Look at the facts.
The Wii U's install base is around 6.6 million. If it continues selling around 60,000 units a week, it'll be around 7 million units when Hyrule Warriors hits. This isn't Wii numbers, but you have to take into account the type of customers that own the Wii U. These are NOT casuals, these are NINTENDO fans. So even if the install base isn't 100 million, Hyrule Warriors will still sell relatively well because of who it's being aimed at.
Hyrule Warriors release date is fantastic. It'll release a few months after the Wii U's biggest franchise (Mario Kart) has been pushing consoles and the new install base is hungry for games. Also, it's close enough to the holidays get more sustained sales down the line when the Wii U gets the holiday bump. This game couldn't have better timing.
For a large majority of Nintendo Fans, this game is NEW and exciting. There are Zelda fans that have never played a Dynasty Warrior's game and seeing the Zelda formula shaken up and looking more action packed is enticing. Also I'm sure some Dynasty Warriors fans will be intrigued by the LOZ mythos being injected into their favorite franchise.
I don't see a scenario where this game sells under 1 million units.







