As far as I know, W is set to be a full length Kamen Rider series, and will continue until next September. There is a rumor out there now that for the 35th anniversary of Sentai (that'd be Sentai 2011), the series will be a short one, like Decade, and this will bring the series back into sync, with September premiers. The rumor stems from Bandai wanting to take advantage of the Christmas season (new toys would be out for Christmas, instead of after.)
So, if this rumor is true, Kamen Rider W will start in September 2009 and all other Kamen Rider series will end in September. The new Sentai 2010 will start on February 2010 and end in August, so the new Super Sentai and Kamen Rider will start September 2010. See, school doesn't start in September in Japan. Super Sentai and Kamen Rider usually premiere in February. While here in America, new shows start in September. Well, they used to. And most children franchises coincide with the school year or summer, in order to ensure sales for Christmas. So, having the two series start in September will be interesting. I like a change. And such an interesting way to start things off. And how will a 6-month Super Sentai series look like? We'll see.