2008 will probably be the earliest we'll see a new generation. At least it'll probably be a 2008 model year in early 2007, given that Toyota has had some early product launches for certain models, 2003 Corolla, 2006 Lexus GS series, 2007 Camry.
The 4Runner isn't on Toyota's typical 5 year product/generation cycle. Toyota typically has powertrain upgrades in the third year and cosmetic upgrades and face lift in the fourth year. Assuming the 4Runner is on the 5 year product/generation cycle, '05 4Runner V6's got the 5 speed tranny and V8's got VVT-i, '06 got the cosmetic upgrades, making '08 the next generation. This is true for most Toyota's that have a 5 year product/generation cycle, i.e. 5th gen Camry introduced in '02, '04 V6 SE got the 3.3 V6 and '05 was face lifted.