According to some sources, Zelda Wii was already in development in 2006, so even before Twilight Princess launching.
So if the game finally arrives at the end of this year 2010, it will have the longest development cycle in a Zelda game: 5 years.
Even longer than Ocarina of time (three years).
Will that be truth?
http://wii.nintendolife.com/news/2010/01/near_five_year_development_cycle_for_zelda_wii