I think koharu will graduate in 2010 but with one condition in 2009 there will be 9th gen audition because i got info from my friend that show me someone blog but the blog already change with different topic. It says the blog writer got some info from someone who close to tsunku and got tsunku note about graduation and audition. In that note if yaguchi mari and fujimoto miki doesn`t retired, they will have graduation like this: 2006-Konno Asami with Ogawa Makoto, 2007-Yaguchi mari, 2008-Yoshizawa Hitomi, 2009-Fujimoto Miki, 2010-Kusumi Koharu but with Yaguchi retired Yoshizawa graduation move forward to 2007 and after Yoshizawa graduation Fujimoto also retired that make from 2007-2009 there will be no graduate. Audition already planned like this: 8th-2007, 9th-2009, 10th-2011, 11th-2013, 12th-2015 but with 2 people retired the schedule of audition, i don`t know if change or not. I think Tsunku will never make someone graduate if the member only 9 because he think 9 people is the minimum number of morning musume just like 2001. 2010 graduation will be the same like 2002 graduation.
2002
2001 - Leader graduate Nakazawa Yuko - member 9 pl
5th gen audition - member 13 pl
2002 - Goto Maki graduate (3rd gen) - member 12 pl
2010
2009 - Leader graduate Fujimoto Miki - member 9 pl
9th gen audition - member ? pl
2010 - Kusumi Koharu graduate (7th gen) - member ?-1 pl
As you see that next graduate will be same as 2002 graduate because Goto and Kusumi came from gen that only 1 member and they already have solo single and album before they graduate. But the 2009 graduate can`t be happen because the leader already retired long before she got be graduate.
wise words!! I never thought Koharu would be the next... But you were right